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Popular Science & Technology (PST) series is being published by DESIDOC to promote the knowledge and understanding of the applications of science and technology in Defence among defence personnel, students, and general public. The contents covered in each of the titles are current to the year of publication.

The basic concept of EW is to exploit the enemy's electromagnetic emissions in all parts of the electromagnetic spectrum in order to provide intelligence on the enemy's order of battle. EW involves a variety of concepts and definitions of many
. The battlefield of electronic warfare is global and its intensity varies according to different national perceptions of potential threats. as shown in Fig. and uses the entire range of the electromagnetic spectrum. Electronic circuits are. some people also call it Electromagnetic Warfare. electronic warfare is a catalyst towards the maintenance of regional and global balances which deter the outbreak of armed conflict. it is not conducted using electrons. intentions and capabilities and to use countermeasures to deny effective use of communications and weapons systems while protecting one's own effective use of the same spectrum. either directly or via television or films. Sir Winston Churchill coined the words 'wizard war' and 'battle of beams'. 1. rather it is electromagnetic. In fact. of course. Because of this. the most accepted term for this field of applied science is 'Electronic Warfare'. A majority of people have seen them in action.e.1 WHAT IS EW? Electronic Warfare (EW) is not strictly 'electronic'. During World War II.1. However. This silent battle of beams is commonly called Electronic Warfare. But there is another kind of invisible fight involving the use of radio and radar emissions which is always going on in the atmosphere. i. almost everybody is familiar with fighter aircraft. Introduction
Today.l. battle tanks.. used in EW equipment. warships and submarines.

Before we go deeper into the study of electronic warfare. when Russian naval commanders attempted to jam radio transmissions from Japanese ships. which embodied the basic terms of EW and their definitions. These are shown in Fig. According to this.
. as electromagnetic energy had been used. the US Joint Chiefs of Staff issued a document. not for communication. in this war. Electronic Countermeasures (ECM) Electronic Counter. in fact. Early techniques were often primitive and it was only from World War II onwards that EW gained an element of sophistication and maturity . the Germans intercepted the communication system of the British forces. it has been practiced in one from or another in every major conflict since the early days of this century. Recognising this problem. World War I saw the widespread use of radio for communication and transmission of combat information. back to the Japanese high command for necessary action. In 1914.2. electronic the espionage. such as false transmissions. is will help to highlight the importance of EW. Direction-finding achieved great success in maritime operations during this war. let us have a look at the historical development of EW and the strategic role it has played in key conflicts. However. 1. It was also during World War I that both sides experimented with electronic deception in its the simplest forms. but for jamming enemy communications. This communication jamming in practice is considered the first real action of EW.Countermeasures (ECCM).2 HISTORICAL DEVELOPMENTS IN EW Electronic warfare is not new. dummy traffic and other similar ruses for misleading the enemy. without getting jammed. The first reported conflict involving the use of EW was the Russo-Japanese War of 1905.terms which make the subject difficult to comprehend by laymen. ever since radio communications were first used in war. the Japanese were successful in trailing the Russian fleet because they could transmit information about their movements and combat formations. the field of EW is most commonly subdivided into three categories: Electronic Support This Measures (ESM).

the Arabs employed a range E of ECM and ECCM measures. The British began to equip their aircraft with both noise jammers and passive ECM equipment as a countermeasure. The 1973 war threw EW into the forefront of modern military thinking. The sophisticated Wurzburg gun-Iaying German radars created a sensation in World War II. The US countered by deploying every available EW aircraft including the EA-68 Prowler . Poor ELINT (Electronic Intelligence) before the war led to the inadequate preparedness of the Israeli Air Force to counter the Arab air defences. they managed to adapt countermeasures to suppress the radar. radar-controlled AAA (anti-aircraft artillery) made their first appearance in the stormy battlefield. there was a fight between ECM and ECCM. Early sys in 1939. some crash programmes were started by the USA to develop an adequate EW capability to reduce the aircraft losses. The race of developing countermeasures against countermeasures continued to be directed to outmanoeuvre and outperform the adversary's equipment and ECM. only to lose it against a new countermeasure. It brought to surface the necessity of possessing a complete range of EW equipment. specialised EW equipment began to be developed only during World War II. Each side momentarily gained the upper hand in EW. The 1973 Middle East War (also known as Yom Kippur War or the Arab-Israel War) saw most of the latest Soviet SAM and AAA systems in action. Use of radar for war the operations was a major development of this period. Like the World War II.However. ECM called 'Bromide' against the German technique of eql dropping bombs on pre-located targets. EW technology became progressively more specialised and sophisticated after World War II. For the first time in modern warfare. the Vietnam War also continued for many years. one may face F disaster. During 'Vietnam War in 1965.Throughout the war. This war clearly emphasised that if one fails to control electromagnetic B spectrum and to gather intelligence. Germans employed Luftwaffi's LZI30 Graf up Zeppelin for locating British early warning radars. after sustaining heavy air losses in the first few days. In 1971. However. Thus the Vietnam War of 1965. one of history's heaviest barrages of radar-controlled AAA and SAMs were employed against US bombing raids over Hanoi and Haiphong. clearly demonstrated the conflict between radar and ECM and between ECM and ECCM. In addition to passive communications monitoring. The rad Germans also introduced radio guidance techniques for their bombers during night raids on British military installations.controlled SAMs and AAA. Under pressure due to this constant threat of destruction. which continued up to 1971.
. Each side used a different region of the electromagnetic spectrum for target tracking and guidance. The US found itself severely short in ECM and early warning equipment to meet this new challenge. he first fully integrated tactical airborne jamming system. To counter this serious threat. the British eventually developed a deceptive out. with an efficiently run Signal Intelligence (SIGINT) service. a dense ground-based air defence E' system featuring the full spectrum of overlappling SAMs and AAA was thus encountered. and the first SA-2 downing of a US fighter aircraft was recorded. Soviet SA-2 'Guideline' radar-guided SAMs (surface-to-air missiles) and 57 mm. even in peace time.

a British Type-42 destroyer. where victory or defeat may come in a matter of seconds. several innovations were employed in ground combat. communications and intelligence (C31) on the part of British forces contributed significantly to its success in the Falklands War. had lost only two helicopters and the Bekka Valley area had been destroyed by the Israeli Air Force without much losses. Two Israeli Grumman. Argentinian forces made very little use of EW systems. including Soviet-built 'Makoyan' MIG-23 fighters and five French-built ' Aero Spatiale Gazelle' attack helicopters.
. was simply unable to get on target in time because of its slower reaction time. What was the decisive factor? Electronic warfare. Another element which contributed greatly to the Israeli success in Lebanon was the coordinated use of AWACS (Airborne Early Warning and Control System) and ECM against enemy command. in turn. control and communications systems.In April 1982. Israelis had employed their 'Mastiff RPV (as well as drones) to ascertain the microwave radio frequencies used by the Syrian SAM. Israeli forces reported the destruction of 86 Syrian aircraft. The Sea-Dart missile system on board Sheffield. On 4 May 1982. Unfortunately for Sheffield. Excellent organisation of command. called C3CM. the world saw another EW conflict in the Falklands War. allowing them to plot their exact location. The classic struggle between the lance and shield. In June 1982. the missile and electronic systems. Thus. was fought between Israel and Lebanon in the Bekka Valley . there were no airborne early warning radars on board in operation on 4 May when the Exocet missiles were sighted close in. remotely piloted vehicles) to know the location and characteristics of enemy operating systems and weapons. known as the Lebanon War. Israeli Air Force played a dominant and decisive role In this war. was the real key to their success. By mid-june. E-2C Hawkeye aircraft obtained electronic bearings of the Syrian missile radar system. the Israelis made use of a special type of deception technique. supported by accurate planning of EW actions. Israeli aircraft then destroyed the sites with rockets riding a microwave beam to the SAM-6 sites. for this type of warship was supposed to constitute the main fleet defence against air attack in cooperation with airborne early warning aircraft to detect low flying enemy aircraft. Skeffield lacked the latest EW equipment capable of countering technologically advanced western missiles like the Exocet. control. In this war. HMS Sheffield. called decoys (drones and RPVs. The entire military world was shocked. even microseconds. except passive EW. The Israelis reported that they.65. was destroyed by a a sea-skimming Frenchbuilt Exocet missile. The outstanding results achieved by the Israelis show that the new concept of real-time warfare. the gun and armour. Electronic warfare today is an utterly deadly battlefield. another fierce EW battle. the countermeasures and counter-countermeasures will no doubt continue in the form of fight between radiation weapons and radiation countermeasures and between these counteremeasures and relative counter-countermeasures and so on. This led to a stunning defeat of Lebanese forces and an incredible victory of Israeli forces. Assessing the war from the point of view of EW. like ELINT and ESM. designed to engage aerial platforms at a distance. in this situation inadequate EW means certain defeat.

. a tank or a warship. or even the difference between life and death.Many technological developments have come about as a result of military needs. Therefore. there are strong reasons for keeping many aspects of EW secret. It revolutionised the areas of research in the academic and specialised research institutions. Today. an attempt has been made to make interested readers aware of the capabilities. an appropriate EW tactic which has been kept secret can mean the difference between the success and failure of their mission. limitations and applications of the diversified science of EW. Radar was the most secret weapon in the hands of military forces. It soon became a household word. Soon after World War II all secrets of radar were thrown open to the public. peace and public good. we have a great variety of radars performing thousands of functions for war. with no significant background in science. students and the general public being informed about the existence and general usefulness of EW. The basic principles. to have engineers and scientists as advisors. to keep EW developments hidden from indiscreet and unscruplous people. This text is thus confined to the discussion of general principles of electronic warfare and its multi-dimensional extension and growth to various areas of specialisations. Since the end of World War II. EW has been one of the best kept secrets with tecnical experts and armed forces. However. to listen to them and utilise his political power to translate their scientific knowledge in to practical wartime technology . An engineer was originally a person who designed and built military fortifications and equipment. Much of the information pertaining to EW is still classified and can be expected to remain so. The common man was interested to know about its capabilities. are easily derived and are easily derived and are unclassified. the intellectual forces of scientific research and development were deliberately and intensively applied to the conduct of war. however. there are equally strong reasons for not only the armed forces and those concerned with National Defence but also the academicians. But during the World War II. though for different reasons. Upto World War II. For a crew of military aircraft. It is still in the interest of these two groups of people.He was also the first leader to recognise EW as a vital phase of military operations. Winston S Churchill was one of the first political leaders. With the same objective in view.

exploit. The deliberate radiation.4 Jamming. or systems is called Jamming.2 Electronic Support Measures (ESM) Electronic Support Measure is that division of electronic warfare which involves actions taken to search for . reduce. in general. ESM is an important source of EW information to carry out electronic countermeasures and electronic. equipment.1. ECM. ECCM mentioned in Chapter 1 have been elaborated. ESM involves. There are two categories of deception. Some of the major subsystems have also been explained.1 EW DEFINITIONS 2.5 Deception.countermeasures. record and analyse radiated electromagnetic energy. 2. absorption. or reflection of electromagnetic energy to impair the use of electronic devices. gathering of EW information through Electronic Intelligence (ELINT).2.1 Electronic Warfare (EW) Electronic Warfare is a military action involving the use of electromagnetic energy to determine. Thus. for the purpose of exploiting such radiations to support military operations. Definitions and Concepts
In this chapter. The deliberate radiation. or prevent the hostile use of electromagnetic spectrum as well as action which retains friendly use of electromagnetic spectrum.1. the general principles of EW are covered.3 Electronic Countermeasures (ECM) Electronic Countermeasures are the actions taken to prevent or reduce the enemy's effective use of the electromagnetic spectrum.1. Two major actions of ECM are jamming and deception. counter.
. or reflection of electromagnetic energy in a manner intended to mislead the enemy in the interpretation or use of information received by his electronic systems is called deception. re-radiation. reradiation.1. Communications Intelligence (COMINT) and ESM receivers. intercept. alteration. 2. 2. 2.1. locate. The terms ESM. 2.

7 Imitative.2.1. effective.
.8 Electronic Counter-Countermeasures (ECCM) The actions taken to ensure friendly. The alteration or simulation of friendly electromagnetic radiations to accomplish deception. or to mislead the enemy in the interpretation of data received from his electronic systems/devices. the field of EW is discussed in terms of active and passive roles. As a matter of convenience and simplicity. 2. use of the electromagnetic spectrum despite the enemy's use of EW are known as ECCM.1. Active EW is the radiation or re-radiation of electromagnetic energy so as to impair the enemy's use of electronic equipment/system. On the other hand.6 Manipulative. Passive EW is the search for and analysis of electromagnetic radiation to determine the existence. Introducing radiation into enemy channels which imitates his own emission. source and pertinent characteristics of the enemy's use of the electromagnetic spectrum.1. 2.

the communication system is jammed or misled by creating false messages. in radar EW. However.9 RADAR AND COMMUNICATIONS EW It is worth mentioning here that the above sub-division of the subject EW into ESM. whereas in the case of communications.
EW tries to achieve the above purposes by adopting the following procedures.1. ESM is Passive EW. Further. employs the electronic devices and techniques for the following purposes. 2. in the case of radar. whereas in communication EW. in the case of radar. For example. usually the transmitter and receiver are located at the same place.ts.1.based. Another difference is that the radar usually uses no encryption for message security. there are some basic differences between the two. there is a two-way range for transmission. ECM and ECCM is applicable to both Radar EW and Communications EW. Also.
• • •
Determining the existence and 'placements of the enemy's electronic aids to warfare Destroying or degrading the effectiveness of the enemy's electronic aids to warfare Denying the destruction or degradation of the effectiveness of friendly electronic aids to the warfare.10 OBJECTIVES OF EW Electronic Warfare. degrading or even dangerous for him Defend one's own friendly use of the electromagnetic spectrum.3 shows the numerous divisions. whereas in case of communications. Fig. sub-divisions and branches of today's complex EW tree. whereas encryption is used in communications for generation of secure messages.In general. whether it is radar-based or communications. 2. and ECCM may be either active or passive. the transmitter and receiver are located at separate places. there is only a one-way range for transmission. the radar system is jammed or misled by creating false targe.
. ECM is Active EW.
• • •
Make full use of electromagnetic emissions released either intentionally or accidentally by the enemy Interfere with the enemy's use ofelectromagnetic spectrum in such a way as to render its use either ineffective.

i. There is always an ECCM for an ECM.1 SOME PECULIARITIES OF EW SYSTEMS The design of a system is based mainly upon its objectives or needs. friendly forces always try to counter the enemy's electronic systems through ECM.2. ECCM) to reduce the effectiveness of friendly systems/equipment. since their primary function is to be responsive to a potential threat or the enemy's immediate action. The ECM and ECCM process resembles a ladder-type advancement. One can never achieve unequivocal superiority through ECM.related interaction between ESM.e. and this process continues ad infinitum. It is a dynamic and closely inter. as shown in Fig. as shown in Fig. This ECM. It is active as well as passive depending upon the nature of threat. ECM and ECCM are electronic equivalants of action and reaction of Newton's third law of motion.. There is always an interaction between friendly and hostile electronic systems in an EW environment. the design philosophy of EW systems and their development cycle do not follow the traditional pattern set by other active weapons and electronic systems and subsystems.2.
. ESM may involve active radiation of a signal to determine the characteristics of the enemy equipment/system and ECM may require a passive reception of the enemy signals in order to decide what signal to counter..e. ECM and ECCM and the Order of Battle. Therefore. causes a counter-countermeasure (i. The effectiveness of EW systems is established only when the enemy electronic systems are present. In combat-like situation.
Also. For example. There are certain salient points of difference between the design and development of an EW system and other electronic systems. in turn.2 INTERACTIVE ROLE OF EW The role of EW is not static. The features or characteristics of EW systems are determined when the features or nature of enemy electronic systems have been known or anticipated.5. EW systems occupy a special position under the category of electronic systems.4. as indicated in the following
• • •
The need for EW systems is felt when the existence of enemy electronic systems has been established or postulated. when the combat environment is either real or simulated. 2.

Therefore. The following are the subsystems in atypical EW system. A functional block diagram of atypical EW system is shown in Fig. true or relative bearing (i. 2.2. development and planning of EW systems.3 Search and bearing equipment. frequency. to give an idea about the complexity of the system. Comprises frequency counters and pulse/spectrum analysers and a video display unit.
Thus. its. The receivers display on a cathode ray tube (CRT) the selected signal.2 A TYPICAL EW SYSTEM From the above discussion. Facilities also exist to feed this
. the period and the total harmonic content of each transmitted pulse. Consists of search and bearing receivers which cover a number of specific radar bands. it is clear that an EW system is unique in its features and design. 2.e. These include the pulse repetition rate (PRR). type of transmission.2. angle of arrival of the signal) and the antenna rotation period (ARP). intelligence) is key to the design.. the pulse width.e. the information on enemy activity and its interpretation (i.4 Signal analysis equipment. the design of EW systems is mainly based on the electronic environment created by the enemy. This equipment measures a number of parameters and their values present in the received signal. if desired.2.•
The future design of EW systems can only be predicted when the anticipated electronic environment created by the enemy is known.6..
2.

e.2. the output from the jammer transmitter is applied to a ferrite circulator with one input and two output ports. keeps the antenna aligned on the selected target. 2.6 Jamming transmission equipment. A special jammer receiver. and the power supplies and control equipment to operate the system. 2.information to a remote data system. The high-power amplifier equipment has the capacity to increase the strength of the jamming signal to at least twenty times that of the basic jamming equipment. servo system. the jamming signal is directed to the target by the antenna.8 Jammer antenna equipment. When a high-power amplifier is not fitted.2. liquid-cooled. receiver antennas and antenna training motor. signal parameters and other relevant data.
. In this subsystem. i. It has the capability of transmitting amplitude modulated (AM) or frequency modulated (FM) noise signals or AM pulsed deception signals when the analog signals from the analysis equipment are fed into it. The frequency power output. The binary coded decimal (BCD) signal data from signal analysis subsystem is fed to this subsystem for threat evaluation and/or storage. the output from the transmitter is applied directly to the transmitter antenna. beam switching unit. 2. Comprises special wide-band and spot tuning microwave circuits operating a power output stage providing powers between 20W and 4OOW. This type of subsystem is only fitted to those systems which can provide the excessive power and complex cooling facilities required by large travelling-wave amplifiers. Comprises a signal processor. tactical indicator to display threat category. transmitter antenna. travelling-wave tube (TWT) amplifier. main receiver. frequency of transmission. Some systems may radiate a combination of pulsed and noise signals. This subsystem processes selected analog signals fed from the analysis equipment and converts them to a pulse code for application to the modulation circuits of a radio communication transmitter. in conjunction with a servo system. high-power amplifier (when it forms a part of jamming antenna). If a high-power amplifier is fitted.7 High power amplifier equipment.2.2. pre-modulator and RF transmitter. a high voltage modulator unit. Comprises a ferrite circulator. pulse code modulation (PCM) encoder. Data analysis computer equipment. oscillator. modulation type arid levels are controlled remotely from the high power amplifier control unit. The jammer transmitter covers the same frequency band as the search equipment. 2.. Comprises a high-power.5 Radio data transmission equipment. Comprises a multiplexer (MPX) and the central processing unit with associated memories.

It can be fitted to ground. on differrent frequencies. by adjusting the blanking level. Its ability to function in an all. They are classified according to their applications. tracking. i. It is playing a key role as a sensor in a variety of forms in the modern weapon systems. transmitter and receiver and the associated concepts are given here. The reflected signals or echoes are picked up by the antenna shortly after the pulse is transmitted. longer is the time before the echo is received. A video blanking system is used with most EW display units. The video blanking facility. The transmitter produces intense pulses of microwave electromagnetic energy at short intervals. radar has been found useful in a great variety of applications. the functions which it is supposed to perform. consisting of many subsystems. A functional radar system consists of four basic elements-a transmitter. and it stands for 'radio detection and ranging'. The basic concepts of radar. minimises the interference produced by radars and all jamming transmitters operating in the friendly EW systems. etc. allows. A device. There are many types of radars today.weather environment at long ranges is unmatched by any other available sensor.2. The acronym ''Radar' was coined during World War II. Radars perform a number off functions like surveillance.. guiding missiles. a highly directional antenna. The time gap between the transmission and the receipt of echo is directly proportional to the distance of the target from the radar. Comprises input processing amplifier. an EW system is a very complex structure. pulse shaping circuit. 2.e. using the same antenna. The various types of radars and their functions are given in Appendix I. duplexer. components and devices. The pulses are propagated outward in a narrow beam from the antenna. the details about some components of the main subsystems like antenna. The noise produced in the system is reduced to minimum through special circuits so as to extract exact information about the target. controlling weapons.
.Video blanking equipment (not shown in Fig. which forms an important element of EW systems. the farther the target. a receiver and an indicator or display.9 SOME CONCEPTS ASSOCIATED WITH EW SUBSYSTEMS As has been seen.2. 6). and strike targets at various distances. flip-flop circuit. 2. detecting targets. Since World War II. pulse amplifiers and a video mixer. However. Radar is a complex system. ship. are also outlined. Radar is the most commonly deployed long range electronic sensor. the simultaneous operation of a receiver and transmitter.10 Radar 'Know your enemy' still remains a valuable military maxim. air and even space-based platforms. to provide further insight into the subject. The electronic components and devices associated with the main subsystems are many and not all of them can be elaborated. It can also work at night when there is little or no ambient light to illuminate the target.

50-300 MHz and Ultra High Frequency (UHF). Very High Frequency (VHF). because of their ability to provide over-the-horizon coverage.. Radar parameters include power frequency. antenna gain. Clutter actually arises due to radar returns from buildings. Smaller the radar cross-section. pulse repetition frequency (PRF). Radar cross-section. 300-1000 MHz are generally used for long distance surveillance. trees. The higher frequency bands like.2. 2.11 Radar cross-section. This is a major obstruction in the proper identification of a target by radar.
. and missile guidance applications.Generally. fire control. (8-12 GHz) and Ku (12-18 Ghz) bands. Thus by reducing the physical size of the target. and the radar warning receiver . Search radars and tracking radars are most often found in one of the higher radar bands. These are specific radiation parameters of a radar that distinguish it from all other radars. adopting proper viewing direction and using special surfaces with reduced reflectivity. Radar cross-section of a target plays a major role in its detection and location by radar. . Ka (27-40 GHz) and millimeter (40-100 + GHz) frequencies are finding increasing use in mapping. The radar frequency bands range from 3 MHz to 300 GHz. radar silence. etc. with S.12 Radar clutter. radars operate at narrow bands of electromagnetic spectrum because of operational constraints. antenna polarisation and antenna scan. Some terms or concepts which are associated with radar and frequently quoted are radar cross-section. radar clutter. C and X bands being the widely used ones. C (4-8 GHz). viewing direction and the composition of the target. one can reduce the radar cross-section of a target (say aircraft) by several orders of magnitude. clouds. generally denoted by the Greek letter -sigma ( ). S(2-4GHz). geometry of the target. plants.13 Radar signature. even of the same type.e. foliage. is the area a target would have to occupy to produce the amount of reflected power (i.making curved surfaces). radar signature. but most of them operate in what are commonly called 'Microwave Frequency Bands'. 2. using effective design in its geometry (i. sea waves.e. Ku (12-18GHz) K (18-27GHz).. radar frequency.2. pulse length. 2. It depends upon several factors like physical size of the target.2. more difficult is its detection. echo) that is detected back at the radar. designated as L (1-2 GHz).

2.2.14 Radar silence. Generally, it means there are no radiations emitted from the radar, and radar simply 'listens' in this mode. More specifically, it is an imposed discipline prohibiting the transmission by radar of electromagnetic signals on some or all frequencies. 2.2.15 Antenna An antenna is a device that can transmit and/or receive electromagnetic energy. In a transmitting antenna, electrons flowing back and forth in the conductor generate electromagnetic fields that propagate far into space. In a receiving antenna, passing electromagnetic fields cause electric current to flow back and forth in the antenna conductor at the same frequency as the field oscillations. Thus, antenna is a special kind of transducer, that converts electric current into electromagnetic energy and vice versa. The performance of a system largely depends upon its transmitting and receiving antennas. If the antenna is badly designed or poorly located, system operation is seriously affected. Like the human eye and other optical systems, the radar antenna is deliberately designed to be more sensitive in a given direction than in the other directions. This serves to concentrate more energy on the target upon transmission, and to increase the receiver sensitivity upon reception. In other words, in a practical antenna, there are usually one or more preferred directions where power detected is usually more than power detected elsewhere. The factor by which a given antenna 's power density is larger than that of an isotropic antenna (no directional preference) in a selected direction is defined as the' Antenna Gain' along that direction. The maximum gain of an antenna is known as the 'Directive Gain' of the antenna. Each antenna has its specific pattern. The directional characteristics of any transmitting or receiving antenna, when graphed on a polar coordinate system, is called the, Antenna Pattern'.An antenna pattern may have just one lobe, or it may have several lobes. The measure of the degree to which the output of a directional antenna is concentrated is called its 'Beamwidth'. Antenna beamwidth is usually specified in terms of horizontal direction, or azimuth, and can also be specified in the vertical plane. 'Bearing' generally refers to the direction of the antenna, such as azimuth or elevation or a combination of directions. Different lobes may have different magnitudes. The strongest lobe is called the 'Main' or 'Major' lobe. The localised weaker lobes or peaks which lie outside the main lobe or beam are known as 'Secondary', 'Minor' or 'Side' lobes. Maximum energy of a signal lies in the main lobe or beam of the radiation pattern, as shown in Fig. 7.

There is another important phenomenon in antenna, called 'Polarisation'. The polarisation of an antenna is determined by the orientation of the electric lines of force in the electromagnetic field radiated or received by the antenna. Polarisation may be linear, or it may be circular. Linear polarisation, again, may be vertical, horizontal, or somewhere in between. In circular polarisation, the rotation can be either clockwise or counterclockwise. The important aspect of polarisation is that if the transmitted wave is polarised, then each receiver must have a matched polarisation in order to receive the signal. Unless stated otherwise, the polarisation is assumed to be matched to the received wave. The practice of varying the polarisation in a random manner is an ECM technique known as 'Polarisation Diversity'. Almost all EW systems require some form of antenna. The special characteristics which distinguish EW antennas from other types ( e.g. radar and communications) are their broad-band wide-angle coverage and diverse beam and polarisation requirements. Depending upon the pattern, there are two main categories of EW antennas-Omnidirectional Antenna (one covering 360 degrees in azimuth) and Directional Antenna. Omni-directional antennas may be narrow-band or broad-band, linearly polarised or circularly polarised, and are used where coverage in all directions is required for warning and or intercept functions. Directional antennas, again may be narrow-band or broadband, and are normally used with linearly polarised or circularly polarised, direction finding systems, high-gain intercept systems, directional jamming systems and radars. Linear polarisation is used when the antenna is of known linear polarisation and it is desired to optimise the gain of the system, or if polarisation analysis is to be performed. Circular polarisation is used when the polarisation of the other antenna is unknown or variable, or if polarisation diversity for any other reason is required. Circular polarisation is used for both the ECM and ESM functions. There are mainly three types of EW antennas: Fixed Beam EW Antennas, ECM Phased Array Antennas, and Lens-fed Multiple Beam Array Antennas. 2.2.16 Fixed beam EW antennas. There are several designs of fixed beam EW antennas. Each antenna has its characteristic radiation pattern. These antennas are mostly used for ESM and ECM applications.

2.2.17 ECM phased array antennas. An array of an antenna is a collection ofantennas, usually dipoles, placed at equal distances along a common line of reference, known as array axis: A phased array is an antenna having a number of radiating antenna elements driven by some form of beam-forming network. The elements are fed with a certain relative phase, resulting in a directivity pattern that exhibits gain in some directions and little or no radiation in other directions. The primary advantage of a phased array antenna in ECM applications is its ability to rapidly (i.e. within microseconds) and accurately point the jamming beam or beams at the victim radars within its spatial coverage angles. The pointing ability allows the use of narrow jamming beams, which magnify the jamming energy focussed on victim radars through increased effective radiation power (ERP). The phased array, 'thus, find valuable application in both airborne self-protection ECM systems and for stand-off EW jamming missions. The accurate beam pointing capability of phase-steered array is also commonly used to provide direction finding with high probability of intercept. 2.2.18 Lens-fed multiple beaIn array antennas. In ECM phased array antennas, the beam-forming is done through phase steering using phase shifters, and the direction of the beam position is frequency dependent. In case of lens-fed multiple beam array antennas, the direction of each beam is fixed in angle and is made independent of frequency by using appropriate time delay steering in each element. These are used in self-protection ECM applications. 2.2.19 Transmitter A transmitter is a device that produces a signal for communication purposes. A basic transmitter consists of an oscillator, a transducer, a modulator and a signal amplifier. The oscillater provides the carrier wave. The transducer converts audio and /or video information into electrical signal on the carrier wave. The amplifier boosts the signal level to provide sufficient power for transmission over the required distance. The amplifier output is connected to an antenna system for transmission. The design of a transmitter depends, to some extent, on its application. 2.2.20 Receiver Any circuit that intercepts (i.e., reception of a signal by an unintended user) a signal, processes it and converts it to a form useful to a person, is a receiver. A receiver usually consists of five or six basic components- an,antenna or receptor, a front end/wide-band filter, an amplification chain/narrow-band filter, a detector, an audio and/or video amplifier and a transducer. When electromagnetic waves strike the antenna or other receptor, alternating current is set up in the conductors. It is then fed to the front end. The front end, wide-band, filter then provides amplification and some selectivity. This is then fed to the , amplification chain. The amplification chain brings up the weak signal to a

2. The above-mentioned architecture is valid for a simple type of receiver.level suitable for operating the detector. which extracts the modulation information from the electromagnetic energy. locate and identify the sources of enemy electromagnetic radiations for the purpose of threat recognition and tactical employment of military forces and ECM equipments. This is then fed to the audio or video amplifier. EW receiver architectures are usually scenariodependent. EW intercept receivers. intercept. electronically-guided weapons are coming closer and closer to perfection and thus constant updating and refinement of EW equipment is required. The wise battle planner should act accordingly. With the endless evolution of applied military technology. which gives the detected signal sufficient amplitude to drive the transducer. Countermeasures. Nevertheless. Their key function is to search. and hence there is no preferred general or universal architecture which is applicable for all types of intercept receivers. Men make the ultimate difference in an EW engagement.2. EW technology has advanced by giant steps. and the developments in EW systems must always closely and appropriately follow developments in the threat. The mere possession of a certain number of ESM or ECM devices is not enough to ensure success in war. A good system with an unskilled operator will always lose to a marginal system with an alert. those historic air combat operations in World War II over the English Channel revealed the same basic lessons as did the conflicts employing more complex systems at a much later time in history.21 LESSONS LEARNED FROM EW CONFLICTS It is quite evident from the above discussions that in the intervening years between 194l and 1982.the ability of a nation to control the three 'R's (recognition. in themselves. reaction.
. or a combination of these things.
• • •
•
No countermeasure is effective for ever. Coupled with imaginative tactics. One must 'recognise' surprises and correctly estimate their effect.2. knowledgeable technician at its controls. driving a set of recording instruments. it is clear that EW is a dynamic field. The transducer then converts the detected signal to a form suitable for listening. It is time-sensitive and time-perishable.22 ROLE OF R&D IN THE AREA OF EW From the earlier discussion. Countermeasures are more effective when used in a 'surprise' mode. countermeasures are decisive factors for victory. 2. viewing. are useful in military operations.
In conclusion. resolution) will tip the ECM/ECCM balance. In EW what works today may not work tomorrow. on the other hand. 'react' immediately by alerting corrective forces to respond and 'resolve' the situation by a military/scientific group effort geared towards a dynamic solution-motivated mission. have to function in a high signal density environment.

It is. However. transmitter. EW and ECW techniques have now become so highly sophisticated that EW personnel must utilise the most modern computer equipment to assist them in complex battle operations. receiver. demands constant. heavy. the winner will be the side that would control best and manage the electromagnetic spectrum best.
. this is a necessary and worthwhile investment for the military forces. this race of technology-win must be backed up by extensive and intensive efforts in R&D for the survival of the military forces and the security of the country. financial expenditure. this investment must be made in peace time because the price to be paid once an unexpected war has broken out will be extremely high. therefore. is playing a key role since the last few years in the development of special threat-oriented integrated EW systems. The battles in Lebanon have proved beyond any shadow of doubt that the result of future battles will depend much less on the quantity of the aircraft. If a potential enemy changes the frequency of one of his radars or develops a new anti-jamming device or makes some important change in the IR guidance system of a missile.Computer. unfortunately. The extremely dynamic and evolutionary character of EW. which naturally includes new developments in the field of electronic technology like antenna. So. for example. But. vital to have regular research and development facilities for scientific and technical research in order to develop the technology necessary to achieve and maintain superiority in EW which has now become an obligatory route to success. If there is a World War Ill. warships or tanks used than on their quality . then the potential opponent has to modify or completely renew his own EW equipment. signal processing and other associated technologies related to EW systems.

the ESM function is reserved for real-time reaction which serves to differentiate between ESM receivers and ELINT or COMINT receivers.e. The key functions of ESM are intercepting (which primarily involves detection.3. Electronic Support Measures
As already defined. Communications Intelligence (COMINT) and Radiation Intelligence (RINT) as its constituent parts. for subsequent intelligence purposes.2 Distinction between ELINT. frequency estimation and direction finding). changing frequency randomly) transmissions are normally used. employ wide-beam antennas with poor side lobes. are relatively powerful.2. such as Signal Intelligence (SIGINT}. This is defined as intelligence derived from potentially hostile communications by persons other than the intended recipients. Top commanders of military forces are generally interested in SIGINT data. COMINT receivers directed against communication transmissions are similar in concept to those designed to intercept radar transmissions (i. 3. 3. COMINT and RINT 3. This is defined as intelligence information that is the product of activities non in the collection and processing.1 Electronic Intelligence (EUNT). such as ECM equipment. non-communication collection of electromagnetic data using ELINT or ESM nun receivers) except that a different approach is required to accommodate the communication signal structure. Also. To avoid jamming. and use modulated continuous wave transmissions.2. Communication systems generally operate on discrete channels.e. 3. which collect intelligence data for subsequent or non-real-time analysis. of potentially hostile. analysing.1 DISTINCTION BETWEEN ESM AND SIGINT ESM is basically a 'tactically' oriented activity. Electronic Support Measures (ESM) is that division of EW that involves actions taken to search for. encryption and frequency hopping (i. SIGINT data generally focuses on producing intelligence of an analytical nature which is not as timecritical as ESM data.. locate. whereas SIGINT is basically a 'strategically' oriented activity. which has Electronic Intelligence (ELINT). COMINT does not distinguish between the categories of message intercepted. ESM is for 'tactical' purposes that require immediate actions as contrasted with similar functions which are performed for intelligence gathering. identifying. non-communications electromagnetic radiations which emanate from other than nuclear detonations and the radioactive sources. since the sophistication of
. and locating sources of hostile radiations.2 Communications Inielligence (COMINT). and immediately identify sources of enemy electromagnetic radiations for the purposes of immediate threat recognition and for tactical employment of military forces or assets. So. intercept.. SIGINT is thus closely allied to ESM. in principle.

when a radar. political moves and covert data collection. The second category of information might be and called as tactical information. like battlefield surveillance. determination of enemy missile launchings. Thus. and RINT is intelligence derived about and from the enemy electromagnetic radiation (i. the function of intercept receivers has been extended from that of a single aircraft detection to the detection of warlike intentions of potential enemies. location. The strategic mission primarly involves protection of a country's national assets from attack while a tactical mission involves the use of operational forces during combat operations. 3.Two classes of information are Important for applying a suitable ECM against the enemy's electronic systems. COMINT is intelligence derived from the emitter. and because of the increasing complexity and sophistication of these weapons. such as which particular ECM tactic should be employed so as to defeat the enemy's mission. which include such things the as whether the enemy is using a certain electronic system or weapon.2.e. The first category of information can be termed as strategic information. a guided missile. 3. even when they are in a non-transmitting mode of operation. a bomb fuse. and recognition of a signal associate with a particular piece of radiating equipment. then it is necessary to know the nature and amount of the interference that may be present in order to design equipment that can function properly. ELINT is intelligence derived about the emitter. Due to this dense operational signal environment. This is defined as intelligence derived from potentially hostile communications and weapons systems by virtue of their unintended spurious emissions.3 Radiation Intelligence (RINT). study of enemy production and industrial capabilities. In brief.
.2.. Study of operational environment also plays an important role in the design of intercept equipment for the detection.4 IMPORTANCE AND PURPOSE OF EUNT/ESM SYSTEMS Electronic reconnaissance (which covers ESM and ELINT functions) and its operational employment play important roles in view of the continuous increase in the number of radars and other electronic emitters. the additional difference between COMINT and ELINT is the additional processing applied to the received signal in an attempt to recover the message. the mode of operation of the system. which include such things as technical characteristics of the electronic systems and weapons to be countered. the frequency of operation of the system and whether the enemy is shifting his frequency as a result of jamming employed. This type of intelligence information is needed to make strategic decisions. and the nature of supplementary systems which can be employed by the enemy. This type of information is needed to make immediate tactical decisions.encryption may not be apparent until decryption decryption is attempted. or an ECM system is required to operate in an environment in which there are many electromagnetic radiators. such as whether one should attempt to counter the system and what characteristics are required for the countermeasure device. activities) utilising active techniques.

In addition. ELINT operations satisfy a variety of requirements. RF . 3. update hostile force electronic order of battle (EOB) information. search. the signature of every radar is collected. pulse width. pulse repetition frequency (PRF).
. is that it is completely passive..In general. An intercept receiver (either ELINT or ESM) is normally used for the collection and analysis of reconnaissance or surveillance data. The most general purpose of the analysis of electronic reconnaissance data is to develop technical descriptions and to geographically locate the various emitters. both during times of peace and war. in order to guide countermeasures to these targets. power.e. evaluate hostile force command and control procedures and a host of other intelligent functions which can help in tactical operations. Also.. Special ELINT systems have been developed which scan each frequency band continuously. aircraft. IR. The latter ELINT effort is made in order to evaluate the enemy defensive weapons. etc. RPVs. ECM and ECCM. tracking). TV or laser) and the ECCM employed. as well as fixed and mobile land-based facilities are used for collection of ELINT . modulation. analysed and stored. ELINT serves a strategic role of the enemy.. They can locate hostile electronic systems and weapons. such as transmitter's frequency.5 ELINT SYSTEMS The primary objective of an ELINT system is to compile operational data on enemy electronic systems and weapons. as well as just prior to and during specific missions. test hostile force ECM capabilities. lasers and sonars at much greater ranges than the maximum range of those sensors. data and telemetry an links. Thus.. employed.e. early warning radars. mode.2. ELINT information is also used for direction-finding or determining the exact location of enemy radars and defences. and to determine the manner in which to conduct the mission. The signature (i.g. obtain information on specific transmitters and emissions. The basic targets of ELINT are all types of radars. determine its signature and compare this with others in a library in order to identify and locate the threat. when used as detector of enemy systems. located and identified by their signatures in their operating modes (e.One of the most Important sources of both strategic and tactical intelligence concerning a potential enemy's operations is the interception and analysis of the signals radiated by his electronic systems. ELINT is usually carried out on a regular basis. satellites. command. perform a real-time analysis of each intercepted signal. ELINT is also used to obtain data on enemy navigational systems. Peace-time operations have the objectives of gathering maximum possible data on the complete electromagnetic environment within specified areas of interest to any one nation. Thus. as well as a tactical role in helping to develop or reprogram appropriate ECM and ECCM equipment to meet each threat. An important advantage of ESM. characteristics) of each radar consists of measurable parameters. Specially equipped ships. the control and guidance techniques used for each weapon system (i. which are detected. it provides the potential of detecting enemy radiations from such sensors as radars.

2. and targeting. avoidance. FM signals.2. 3. The principal job of an ESM receiver is to provide information on the existence and nature of various signals usually in the minimum possible time. frequency estimation and direction finding.. to provide a source of information for immediate reaction involving ECM. Direction-finding is achieved by using special DF antennas. channelised radiometer or the cross correlator Frequency estimation is achieved by using ESM receivers. Radar warning receivers are used in military aircraft and helicopters to warn of attack by surface-to-air and air-to-air missiles. They
.e.7 Radar Warning Receivers An important example of an ESM system is a radar warning receiver (RWR) which intercepts radar signals and analyses their relative threat in real-time.. which collects and records for subsequent analysis as much data as possible on enemy non-communication equipment.e. However. Detection is achieved by using radiometer . i. real-time environment. The EOB is obtained through ELINT or electronic reconnaissance.6 ESM SYSTEMS The primary objective of an ESM system is to intercept the enemy electronic systems in a tactical. single sideband (SSB) signals?
The list is almost endless.e. These three elements of interception are usually integrated in a practical system.. ECCM. the aim of an ESM system remains the same. To accomplish this analysis. An intercept system (i. i.3. the RWR must have a threat library representing the enemy's electronic order of battle (EOB. Interception of hostile electronic environment is generally attempted to achieve three basic functions-detection. No single ESM receiver will answer all such questions. air interceptors and anti-aircraft gun systems. a document describing where and when specific enemy electronic systems are being or will be used in a given battle situation) stored in its microprocessor. which provide measure of angle of arrival (AOA) of emitter pulses. ESM receiver) can answer one or more of the following questions:
• • • • • • • •
Are there any signals present? What are the electrical characteristics of and directional bearing to those signals present? Is there a particular signal present having certain prescribed characteristics? Is there a signal present which is tracking the location of the intercept receiver? Is there any new signal added in the general signal environment? Is there an unusual signal (not seen 'in catalogues) present? Is there a signal present that shows the characteristics of motion of a target? Are there CW signals.

pulse rise and fall times. Each receiving system has its own relative advantages and disadvantages for a specific application as discussed in the following.Ideally. process and display all signals of interest to meet its specific mission requirements. no single ESM receiver or antenna system can gather signals over the entire frequency spectrum of interest. to foil the attack. etc. frequency. pulse width. The more elaborate radar surveillance ESM receivers are similar in concept to RWRs. scan type and rate. Radar warning receiver is generally the simplest form of ESM receiver consisting of an unsophisticated low-sensitivity equipment. The complexity of modern ESM receivers is increasing to cope with the continually expanding dense signal environment.. The above requirements are hard to satisfy for the total range of signal parameters involved. polarisation. These ESM receivers have excellent multiple signal handling capability in a dense emitter environment.
. It needs filtering or sorting of emissions in order to classify each signal to know the important parameters like the amplitude.. of the radar. Thus. the intended target may take some evasive manoeuvres or employ deceptive countermeasures. 3. polarisation. etc.2.are also used to warn tank crews and submarines of imminent threat. frequency. an ESM receiving system should be able to
• • • • • •
Intercept a transmitted signal at any frequency Determine the types of modulation in the signal Identify the usable intelligence carried by the signal (i. and they are used to map enemy radar and communications installations and to monitor radio messages. chaff or flares. PRF. Their probability of intercept (i. direction and relative priority of the threats. with dense signal environment. ESM reconnaissance or surveillance receivers are generally considered more complex than RWRs. except that they generallv employ more sensitive receivers to intercept radar radiations at long ranges. an ESM receiving system must gather . traffic analysis. and measure additional radar parameters.
In brief. and statistical characterisation of features (like frequency. scan modulations. such as coherency .8 Advanced DM Receivers It is difficult for the simple radar warning receivers to cope . coherency . amplitude) Accurately measure the direction of arrival of the waveform so that the location of the transmitter can be calculatcd Process and preserve the signal characteristics for later in-depth analysis Provide significant information to the operator (and/or computer) to enable him to make intelligent and timely mission decisions. Once alerted to the type. pulse width.). have a higher direction-finding accuracy. pulse train characteristics. particularly when many emitters are present in the dense environment. angle of arrival. as appropriate. Many advanced ESM receivers have been developed on the basis of various design approaches.e. For example. intra-pulse modulation.e. polarisation. performance) deteriorates.

3. inability to handle a very high data rate. minimum pulse width that cannot go much below 0. However. the analyser has to handle a wide open system and cannot readily handle complex and dense signals. 3. However. On the other hand. 3. proven design and handling of frequency agile signals.2.
. and are basically incapable of handling frequency agile systems. they cannot handle frequency agile signals. high selectivity and high senstivity.3. the systems suffer from many limitations. easy jamming. limited resolution. 3.and cost-effective manner .12 Channelized receivers. but suffer from their limitations of requiring a channeliser .2.2. they cannot do monopulse DF in a size. require channelisers. and again requiring multiple receivers for DF and a very wide IF bandwidth. In general. slow search speed. are susceptible to ECCM.2.10 Superheterodyne receivers.2. 3. However. They have the advantages of high probability of detection. measure pulse width.14 Acousto-optic Bragg cell receivers.11 Microscan receiven. simultaneous signals and CW signals.They are low cost. They have the advantages of high selectivity. They have the advantages of proven technology . very good frequency measurement accuracy .13 Instanteneous frequency measurement (IFM) receivers. low frequency resolution and needing multiple receivers for direction-finding operations. small in size and are doing well in limited applications. but suffer from their limitations of coping with agile signals. Their capability is limited for fine frequency measurement. and require two receivers to do monopulse DF and the hardware is still unproven. They have the advantages of high probability of detection and the ability to handle wideband signals and frequency agile signals.9 Crystal video receivers.1 microsecond. proven design and not being susceptible to jamming. they suffer from their limitations of limited frequency accuracy. are slow in searching. They have the advantages of high selectivity. They have poor sensitivity. high probability of detection.2. they suffer from their limitations of poor sensitivity. and not being susceptible to jamming. They have the advantages of high probability of detection. and their requirement of a channeliser.

a military force generally practices emission control (EMCON).e. navigation. radar.
.2. Friendly forces or systems. by tactfully managing their electromagnetic radiations. good sensitivity. So. handling frequency agile signals.15 Surface acoustic wave (SAW) receivers. try to achieve maximum advantages in the area of intelligence data reception..16 COUNTERMEASURES TO ESM SYSTEMS To make ESM systems ineffective. doing monopulse DF with a single receiver and being hard to jam. Active or radiating weapons are usually designed in such a way that the active sensor (i. They have the advantages of high probability of detection. guidance.) is only turned on for its terminal phase (of . having good high-dynamic range (i. it is evident that there is hardly any single ECM receiver which can be employed for all purposes. which restricts emission of electromagnetic radiations until it knows that it has been detected.2. identification.e. an indicator of the signal variations that the system can accept. and reproduce. etc. Completely passive weapons such as anti-radiation missiles and heat-seeking missiles provide no warning for ESM systems.. In practice. and basically the hardware is still unproven. minimum pulse width. handling multiple signals. From the above discussion. without objectionable distortion). either a hybrid approach or a combination of two or three receivers is used to exploit their relative advantages to handle effectively the dense signal environment. etc. friendly forces are to be always very careful and alert while using ESM systems for collection of strategical and tactical information about the enemy weapon systems and the forces. over hostile forces or systems in a given situation through emission control.3. 3.he order of 10-30 seconds) so that minimum warning and reaction time is given to the target. sonar. The limitations of the receivers are that they take moderate time to resolve pulses that are close together. detection.

4. ESM and communication systems. This ECM mission may be achieved either by jamming. iv. More comprehensively. structure. radiating) ECM and Passive (i. ActiveJamming may be either Noise Jamming or Deceptive Jamming whereas Passive Jamming may be achieved by chemical or mechanical means. non-radiating) ECM. composition or activities of friendly forces within the radar coverage.o accomplish timely and accurate detection.e. tracking of radar targets and to recognise. techniques or methods are used to prevent or reduce the enemy's effective use of the electromagnetic spectrum. deception or disruption. Within each class of jamming. Further. These means may be used to either deny him the information he seeks.
ii. This wide range of techniques is illustrated in the form of a chart in Fig. Saturate threat systems' data processing and operator capability t. are actions that are taken to prevent or reduce the enemy's effective use of the electromagnetic spectrum. there are two major techniques or methods of ECMActive (i. deceptive data into hostile electronic systems to generate ineffective responses by automated electronic systems. there are different techniques used for denial or deceptive purposes. as already defined. Destroy hostile electronic systems so as to deny s hostile forces the use of key elements of their radar sets and C3 (command. iii.. ECM may also be used to enhance one's own weapon systems' effectiveness. Prevent data acquisition and dissemination by hostile radars.. i. Introduce false. or to give him false information or to overload his computing capacity with so much false data as to degrade the performance of his system and make it unable to perform its intended mission. As can be seen from the figure. process and communicate essential elements of information. and to generate ineffective personnel or command and control actions. there are four basic ECM operational objectives. Electronic Countermeasures
Electronic Countermeasures (ECM). control and communications) structure.
.8.e. are thus means of interfering with the enemy's electromagnetic activity. ECM. and prevent hostile ESM systems and communications from receiving information regarding the operation of friendly forces. by denying them information regarding the presence.
A number of ECM tactics.

all the power output of the jammer is concentrated in a very narrow bandwidth. 4.4 Barrage jamming.3 Spot jamming.4. Within the general class of noise jamming. all the power output of the jammer is spread over a bandwidth much wider than that of the radar signal. The primary advantage of noise jamming is that only minimal details about the enemy equipment need be known. also called 'point jamming' or 'narrow-band jamming'.This may be achieved either by noise jamming or by deceptive jamming.
. In other words. there are three different techniques for generating noise-like If interference. 4.2 Noise Jamming The objective of noise jamming is to inject an interference signal into the enemy's electronic system such that the actual signal is completely submerged by interference. This type of jamming is also called 'denial jamming' or 'obscuration jamming'. In this type of jamming. Spot jamming is usually directed against a specific radar and requires a panoramic receiver to match the jamming signal to the radar signal. In this type of jamming.1 ACTIVE ECM This involves degradation of the effectiveness of the enemy system by generating an transmitting electromagnetic energy . 4. ideally identical to that of the radar. it involves the massive and simultaneous jamming of the whole of the frequency band.

In this case. but all other transmission parameters is required. It is generally true that the bandwidth of sweep jamming is wider than that of the barrage jamming. For deception jamming. sometimes as much as an octave (a 2: 1 band)..7 Range deception.e. Deception jamming can either be manipulative. an exact knowledge of not only the enemy radar frequency. The actual difference between barrage and sweep jamming lies in the modulation techniques and size of the' frequency band covered. Deception jamming is generally used for self-protection applications against terminal threat weapon types which employ tracking radars. This technique..4. This is also similar to barrage jamming.
. Barrage jamming often uses an amplitude-modulated signal covering a 10 percent frequency band (i. whose objective is to obscure the real signal by injecting a suitable level of noise-like interference into the victim system. Range deception jamming is used to foil missile guiding radar systems where the tracking radar guides the missile (or other defensive measures) to the target in range by locking a range gate on to the target.the power output of the jammer (i. Both barrage and sweep jamming are used when the exact frequency of the enemy system is not known. to degrade that system. 4. where friendly emissions are altered or simulated to mislead the enemy. and hence. This range gate delays the target echo and its position is relayed to the missile to be used for intercept information. or imitative. jammer frequency) is swept back and forth over a very wide bandwidth. In other words. Sweep jamming often uses a frequency modulated signal and the frequency is swept back and forth over a wide frequency bandwidth. in away . three main electronic techniques to return false signals have been developed.e. bandwidth equal to 10 percent of the central frequency). These signals have characteristics similar to those of the radar.5 Sweep jamming.6 Deception Jamming The objective of deception jamming is to mask the real signal by injecting suitably modified replicas of the real signal into the victim system. velocity or azimuth. thereby deceiving the radar into erroneous conclusions about range. this type of jamming is used to introduce false signals into the enemy's system in order to deceive or confuse. Within the general class of deception jamming. One major disadvantage of this form of jamming is that it requires much more output power than spot jamming. is spot or point jamming of a more intelligent nature. where false information is introduced into enemy receivers by imitating his signals. 4.. This is in contrast to noise type of jamming. but the relative bandwidth is often determined by the hardware used.

The main reason for the higher complexity is that their performance characteristics must be more closely matched to those of each type of the system to be jammed than the performance characteristics of a noise jammer. This is another deceptive ECM technique that degrades a tracking radar's ability to develop the correct azimuth and/or elevation data of a target. 4.The techniques of range deception. called 'inverse gain radar repeater' is normally used to deceive a conical tracking radar. the CW ( continuous to the wave) illuminator signal is detected by the jammer and a exact false. 4. used When the radar has been led far enough away in frequency. called a 'range gate stealer'.9 Azimuth (or angle) deception. Deception jammers are generally more sophisticated and of higher complexity than noise jammers. An azimuth deception jammer. In the deceptive velocity jammer operation. A hybrid type of jamming which incorporates some of the features of both spot or barrage noise and deception jammers is called a 'smart noise jammer'.10 Smart noise Jamming. the Doppler shift is interfered with. This is a repeatertype jammer used in a transponder (a device that sends a signal whenever It receives a certain command from a distant station) mode to generate responsive noise ten (the signal sent out by the transponder is called the 'response') over a short span of range. In velocity range deception. This technique repeats a replica of the received signal with an induced amplitude three modulation which is the inverse of the victim radar's have combined transmitter and receiver antenna scan patterns. both in advance and in the course of the actual jamming mission.
. The radar locks on to the incorrect Doppler signal and the jammer slowly sweeps the false signal's frequency more away from the actual Doppler frequency of the target. This type of jammer generates a noise burst which is 'on' before and after the actual target return thereby covering the true return. velocity deception and angle deception can also be applied against surveillance radars. 4. There is also a need for more detailed knowledge of the victim system's performance parameters and modes of operation. This type of jammer allows a low powered repeater to respond to a number of threat radars by time sharing. synchronised to the victim radar. strong Doppler-shifted signal is sent back to the radar. attempts to break the tracking lock on itself by capturing the radar's range gate with a false echo and then moving it off to a false range (time) location.A range deception jammer.8 Velocity range deception. the jammer is turned off and the radar is once more left without a target. This need can be met using ELINT equipment in order to provide real-time analysis of the system's transmissions.

take aim unseen. dust. and thereby avoid enemy fire until ready once again to come forth and battle. 4. has caused a resurgence of interest in recent times. in fact. visual sighting was the only means of locating and aiming at enemy gunners. However. Aerosols. Chaff and flares are the important examples. Long before radar had become the mainstay of battle operations.12 Chemical Jamming Smoke is the oldest countermeasure known to man. particularly against laser threats. In its broadest sense. MBA aerosol having TOP of 5900 ft2/lb.e. the German naval forces retreated under cover of smoke in order to protect their decimated flotilla from further losses. depending upon the particular effect desired. This type of jamming is also sometimes called 'Expendable Countermeasures' (means an ECM device which is used up in its employment). Some forms of aerosols can partially absorb microwave signals also. behind which friendly forces could then deploy. Aerosols are the best chemical agents that are used as smoke. Only some specifically selected chemical materials are fit for this purpose. In the battle of Jutland in World War I.11 PASSIVE ECM This involves deception of enemy's system by employing confusion reflectors. The objective of a jammer look-through mode is to allow the operating jammer to determine its own effectivness. they decrease the level of energy available for the functions of seekers or vision enhancement devices). such as correct tuning and sufficient power level. The aerosol particle size and type are chosen in such a way that it allows both scattering and/or absorption of radiations from electro-optical system targets. One way to confuse enemy gunners was to 'lay smoke'. the scattering effect usually is the dominant source of attenuation for a countermeasure application. mist or fog. The use of 'smoke'. aersol material) in use are those using either white phosphorus having total obscuring power (TOP) of 6600 ft2/lb. are fine solid or liquid particles dispersed in the atmosphere.Modern ECM systems employ a 'look-through' mode to provide periodic monitoring of the threat environment while simultaneously jamming multiple emitters. They are used as obscurants (i. to intentionally generate large clouds of billowing smoke. Thus aerosol particles both scatter and absorb light. This may be achieved either by chemical or mechanical means. while it is simultaneously jamming the victim emitters. it not only uses the expendable passive ECM devices but also expendable active devices. 4...
.e. that is. hexachloroethane (HC) having TOP 4450 ft2/1b or fog oil having TOP 3200 ft2/lb. The entire family of aerosols are not used for countermeasure applications. The most common types of smoke (i. These latter devices may be either jammers or deceivers.

valuable. There exists today an electronic equivalent to 'smoke'.9 and appears on enemy radar screens either as a blot (i.14 Chaff. to diffuse the coherent light beam used in a laser is still being widely investigated by researchers for defence applications. This is usually obtained by using resonant size particles with a high index of refraction.An automatic or remotely operated system can provide quick. as in the case of smoke. RPVs.. or thin metal foil or wire. or as hundreds of false targets around the real one. This effectively breaks the track of radar guided missiles. temporary protection cloud in the immediate presence of threat. The use of aerosols or smoke. The chaff forms a cloud of metallic dipoles.
. it is called 'chaff ' (during World War II. ships or vehicles.13 Mechanical Jamming This involves deception of enemy's electronic system by use of specially designed mechanical objects. as shown in Fig. etc. Cartridges packed with large quantities of chaff of different sizes are dispensed from aircraft. Israeli boats used rapid blooming chaff to screen themselves from the radars of Syrian gunboats equipped with Styx missiles.To be more effective. ground-based targets against visual and laser-directed air-to-ground weaponry . drones. flares. called 'window'). the dimensions of which correspond to half a wavelength of the frequency used by the enemy radar. In this sense aerosols are somewhat similar to chaff. 4. In 1973. it reflects electromagnetic energy to confuse or deceive an enemy system. clutter) masking the real target.e. 4. Instead of scattering or absorbing electromagnetic energy.
Chaff consists of either thin metallised glass or plastic rods. These ( include such objects as chaff. Aerosols are ideally suited for the defence of small. the suspended aerosol or resonant particle should have a small mass and a large scattering cross-section.

Chaff is usually packaged in units about twice the size of a cigarette pack. The flares are dispersed when the heat-seeking missile approaches its target to divert the missile from its target..e. similar to a tuning fork. Thus chaff is both frequency-and orientationsensitive. strategic aircraft and ships. In essence. An analysis of the action of chaff shows that for maximum signal return one should make its length a multiple of one-half wavelength of the radar signal.10. the more pronounced and frequency-specific is the resonance effect. Both these characteristics are compensated for by the typically small cross-section of chaff. one can use chaff of several different lengths in the same package to be effective against radars of widely different frequencies. analogous to that which occurs with sympathetic vibration of a tuning fork or piano string. If a stronger echo is needed. then two or three units are dispensed simultaneously. 4. which means that large quantities of chaff can be packaged in a small volume. A flare is a pyrotechnic (i. Chaff is generally used to protect tactical aircraft. the radiated energy is strongest broadside to the individual chaff element. When this unit is dispensed in the atmosphere it creates a radar echo similar to that of a small aircraft. Also. It is also observed that the thinner the chaff. This length maximises the sympathetic electrical resonance effect. each chaff element behaves like a single dipole with a doughnut-shaped pattern. This is illustrated in Fig. Thus their effectiveness becomes ominidirectional. the chaff elements are randomly oriented upon dispensing.The dimensions and physical orientation of chaff is an important consideration in its design and use. Because of their small size. like fireworks) target launched from an aircraft or other vehicles causing infrared homing missiles or other optical devices to be decoyed away from the true target.
. Thus.15 Flares.

projectiles and other aircraft-type vehicles) are usually smaller than a typical aircraft target. An RPV is an aircraft platform that is under remote but direct control. etc. other means of deception that have become increasingly popular are RPVs ( remotely piloted vehicles) .Most dispensers used for chaff can also be used to drop infrared flares capable of confusing heat-seeking missiles. usually with some form of radar target size augmentation. they are made to follow the most deceptive path away from the real target. dropping expendables or decoys (low-cost vehicles. radar signal repeaters. battlefield communications jamming and air defence radar jamming. or performing other ECM related tasks. The active miniature jammer of low cost and limited power output is also an expendable like chaff. gliders. Delivery of such a small active expendable jammer could be accomplished using rockets. For example. drones and special projectiles containing chaff. controlled rockets. 4. but are made to appear larger electronically. RPVs. The jamming equipment may consist of simple jammers. flares or jamming equipment are also widely used to deceive the enemy. With either passive or active expendable ECM systems. that fool the hostile force into thinking that the decoy is a larger and higher-value vehicle) . flares also playa role in protecting strategic bombers. artillery. In recent times. All this information is quite vital to those forces which are trying to counter such a radar threat. Consequently. In addition to protecting tactical aircraft. to ascertain the microwave radio frequencies used by the Syrian SAM-6 surface~to-air missiles. The main objective of these decoys is to draw enemy fire away from the real target. The net result is delay or confusion in the detection of the real target.16 RPVs/drones/projectiles. In other words. parachutes or the jammer could be contained in a remotely piloted mini-vehicle (mini-RPV). This ECM technique finds valuable applications in off-board jamming of anti-ship cruise missile. RPVs normally utilise drones. this tactic of using RPV s was employed by Israelis in the 1982 Lebanon War . deception jammers or systems which simulate the target's electromagnetic signature.The intention is to trigger con' the enemy radar. the objective against radar threats is to provide a time window in which the target is shielded from radar detection
. small boats. thus forcing them to reveal their presence.e. acting as decoys themselves. trucks or other unmanned remotely piloted vehicles as ECM support to assist strike vehicles in penetrating radar-missile-defended target areas by jamming. The placement of these active miniature multiple jammers in the vicinity of the threat emitter saturates its receiver and overloads its data processing system. the radar's electromagnetic signature). these decoys (RPVs.. ejecting chaff. Early infrared (IR) weapons were very vulnerable to decoy flares. drones. while a drone functions with a pre-set sequence and has no remote control. mortars. balloons. drones and some special type of projectiles. but most recent designs use flares or dual operating frequencies in order to estimate roughly where the peak level of IR output lies. flares. which were later on sucessfully destroyed on their sites by the Israeli forces. location and operating characteristics (i.

This generally occurs in the lower frequency range. 4. Following a. Keeping this in view. and still the most widely used radar ECM technique. all surfaces are made either cylindrical or conical. Active expandable jammers can use either noise or deception jamming techniques. and hence tend to be used where passive systems are not very effective. thus reducing the possibility of reflections. it is not unusual for the broadside radar cross-section of an aircraft to be as much as 500 times greater than the nose-on cross-section.e the important means for the reduction of radar cross-section of a target. with the results conjured up in a single world 'stealth'. as shown in Fig. Of the passive expendable jammers. the radar echo will be small for a mono-static radar. Echoes from curved surfaces are smaller as compared to echoes produced from the flat surfaces because the resonant effect is less and the resultant re-radiation will be distributed in several directions.17 RADAR CROSS-SECTION MODIFICATION Another class of ECM includes such techniques which allow drastic reduction of the radar cross-section of a target. called 'rope'. This may be achieved by use of some specific mechanical and chemical means. The effect of surface curvature of an aircraft also depends on its orientation with respect to the radar. Where possible. non-resonant streamers.
. modern aircraft are designed to minimise the amount of flat surface area which might act as a good radar signal reflector. thus its radar echo will be largest for a mono-static radar. In practice. where chaff dipoles are no longer practical because they require long (about 750 feet). Another advantage of expendable ECM systems is that they are operated from a distance .18 Proper Design Design of the target (say aircraft) and its orientation plays an important role in the reduction of its radar cross-section.. without involving much risk.and tracking. usually below I GHz. because of their simplicity. then not only is the effective cross-sectional area minimum. A great deal of research has been done in this area. However. when the aircraft is broadside to the radar it will look mostly like a flat surface. if the aircraft is nose-on to the radar. Active expendable ECM systems are generally more expensive than passive expendable ECM systems such as chaff or radio-directive decoy reflectors. Reduction of radar cross-section of a target decreases the possibilly of its detection by the radar. chaff is the oldest. I 1 . For example. Thus. but the surfaces are most doubly curved and the major re-radiation will be to the side. 4.

on the other hand. Many non-metallic materials such as mono-filament carbon-reinforced material and new types of fibre glass have proved to be very effective as radar absorbent materials. deception makes no attempt to conceal the aircraft. rather. there are two basic types of radar ECM. jammers have a simpler data processing requirement. jamming and deception. and conceal the aircraft at the expense of requiring more power. 4. a simple signal requirement. the major portion of the electromagnetic energy is absorbed instead-of being reflected. has a smaller power requirement per radar at the expense of more stringent signal waveform and data processing requirements. it seeks to distract the attention of the defence system through false or misleading information.20 MODERN ECM SYSTEMS As discussed earlier. making it difficult to locate the object. In addition.Credible target Echothrough Passive detection broadening Passive detection Jamming Spot jammer Barrage jammer Sweep jammer
(iii) (iv) (v)
(vi)
(vii)
From this Table it is evident that.4. Such special electromagnetic absorbing coatings are given to the outside of planes.
. The general characteristics of each type are summarised in Table I. much like a man wearing a black suit at night. in general. Deception. Thus.19 Radar Absorbing Material To reduce the radar cross-section of an aircraft still further the aircraft skin is coated with an electromagnetic absorbent material. also called 'radar absorbent material' (RAM). Table I: General characteristics of the two basic types of radar ECM (i) (ii) General type Equipment types Deception False target Generator Repeater Gate-stealer Track breaker Primary effect Deny position and velocity Produce false position and velocity Signal type Dissimilar to radar echo Similar to radar echo Data processing Frequency set on False position False required by jammer velocity Frequency set on Power required by Proportional to radar peak Proportional to number jammer power of false power targets and radar coverage power Primary problems Minimum effective range Credible motion Frequency Coverage Look.

iv. However. The high threat density of these types of emitters requires that the ECM system operate under computer control. The essential
. 4. early-warning and ground-controlled intercept radars. A digital computer which compares the threat data against a pre-stored threat library and establishes the prioritised response to each detected threat.
The role of the digital computer is central to all modern ECM systems.21 COMMUNICATIONS ECM The discussion up to this point has emphasised ECM against radar targets. A signal processor which filters the threat data to determine the characteristics of each threat. It assimilates all the collected threat data and compares them against stored threat data to make a decision on the relative priority of each threat. This is the most prevalent type of ECM which is employed in the airborne or ship-based systems.Modern ECM systems are designed to detect. and air-to-air missile fire control radars. A i. iii. by noise jamming. A modern ECM system is intended to counter surface-to-air missiles. Typical ECM systems include both interception and direction-finding (DF) capabilities. and to direct timely (within milliseconds) jamming responses automatically against these threats on a priority basis. v. time. A jamming logic which acts.g. as a control switching matrix to select the proper jamming transmitter and point the steerable antennas (i. ii. particularly the netting. phased array) at the threat or select the proper fixed antenna sector . VHF and UHF radio transmissions used by the enemy in forward battle areas. typical modem ECM system consists following functional parts. It provides real-time solution to the complex problem of allocating the jamming resources of the ECM system in the spatial. The more advanced current ECM systems are designed specifically to cope with pulsed and CW radars. in land-based systems. Also.
An ESM system which intercepts and develops attributes (e. the density and methods of operating tactical radios. anti-aircraft guns. A major reason for this is that intercepted communications traffic becomes a major intelligence source for the commander. power and spectral domains. A technique generator which translates the prioritised response into appropriate modulations suitable for applications to the jamming transmitter. classify. vi. a major part of EW activity is the interception and location of short range and low power HF. Jamming transmitters and antennas covering the concerned bands of interest. which functions to distribute the jamming resources in an efficient manner. and identify hostile radar threats.. is different from radar. and to degrade. pulse descriptors) of the threat. The philosophy of ECM against communications emitters is somewhat different than that against radars.e.

or electronic jamming. Once a tactical communication emitter is located.ingredient of communicaions jamming is radio direction-finding. These are: physical destruction. there are three options open to battlefield commanders. intelligence exploitation. An accepted military principle is that enormous tactical advantages can be gained b-y jamming or feeding confusing signals into the enemy forward communications net than by its actual destruction.
.

A radar antenna having very . side lobes in its spectrum is an important ECCM design technique. shown in Fig. Electronic Counter-Countermeasures
Electronic counter-countermeasures (ECCM) is defined as actions taken to ensure friendly use of the electromagnetic spectrum against an EW threat. a wide range of ECCM techniques are employed. receiver's probability of intercept. pulse length. are discussed in terms of spatial. which in turn. transmitter.1 ECCM TECHNIQUES Many ECCM features are incorporated in the radar design.12. ECCM is mostly concerned with techniques which are embodied in the design of electronic equipment (e. radar and its constituent parts like receiver. 5. etc.
. Most of the ECCM techniques are based on the characteristics of transmitted radar pulse. Some of the spatial ECCM techniques are mentioned in the following. spectral.g. antenna polarisation. Some of the important techniques. ) while ECM usually requires a separate item or unit of equipment which operates in its own right and not as an adjunct to another system. temporal and netting domains. 5.. Ultralow side lobes prevent a jammer deceiver from affecting the radar at many azimuths.1.1 Spatial ECCM This category of ECCM includes techniques which are space-based. Thus ECCM is the art of reducing the effectiveness of an EW threat so that the cost of effective EW becomes prohibitive for the enemy. depends upon the radar parameters like power. Low side lobe levels also make the job of anti-radiation missiles more difficult. antenna scan.2 Ultralow side lobes. etc. 5. Thus ECCM is mostly concerned with the discussion of various radar design principles that have been developed on the basis of various ECM threats which a particular radar system can possibly encounter. frequency. There is one fundamental difference between ECCM and ECM.5. antenna gain.1. Today. PRF.

for use on a surveillance or tracking radar. This is also a radar ECCM and anti-interference technique that prevents some of the unwanted pulse energy entering the side lobes of a radar antenna from adversely affecting the radar's operation.1.e. as distinguished from techniques such as lobe switching or conical scanning.. the performance of this device is not very effective. This technique also employs the same antenna and receiver configuration as the SLB. This technique is very effective in removing deceiving signals. and. has little or no effect on the monopulse tracking operation.1. but less gain than the main beam. is blanked. This is another radar ECCM technique.channel (plus receiver) has slightly higher gain than the side lobes of the normal channel. This device employs one or more auxiliary antennas and receivers to allow linear subtraction of interfering signals from the desired output if they are sensed to originate in the side lobe of the main antenna.3 Side lobe banking (SLB). it is blanked from the output signal. i. however. Except the target signal. The omni. 5. This device employs an auxiliary wide-angle antenna and receiver to sense whether a received pulse is from the side lobe region. self-screening jamming. This technique uses an omni-directional antenna and compares relative signal strength between the omni and the radar antenna. This is not the case with sequential lobing or conical scanning. If so. This technique is quite effective against a single noise jammer. all false signals entering the side lobe of the main antenna get cancelled at the output. which can be easily jammed. therefore. With multiple jammers at various azimuths. any signal that is stronger in the omni-directional channel must have been received from a side lobe. except that a gain matching and cancelling process takes place.
. This is a simultaneous lobing radar technique that measures both azimuth and elevation directions of a target on the basis of a single pulse.5 Monopulse technique. in which angular location of a target is done on the basis of multiple pulses. This technique of angle-tracking a target is inherently a strong ECCM feature. Therefore.1. 5.5. that prevents some of the unwanted noise jamming energy that enters the side lobes of the radar antenna from adversely affecting the radar's operation. because amplitude modulations of noise or of repeated radar pulses from an ECM unit aboard the target.4 Side lobe canceller (SLC).

the transmitted signal is spread over a large frequency band in such a manner that the the enemy ESM receiver finds it hard to detect the signal.. radar-to-target slant distance).
. Pulse-to-pulse frequency shift. so it is very difficult to jam such systems.1. Thus. Phased array radars are quite ECM resistant. In spread spectrum transmissions. It attempts to escape detection by an intercept receiver through a combination of actions. 5. or changing the transmitter frequency radically during every interpulse is the ultimate in frequency agility.7Spectral ECCM This category of ECCM covers frequency-based techniques. The idea is to illuminate targets in a jamming environment with high amounts of average power to increase the detection range of these targets.5. This is the main objective of LPI radar. 5. A burn-through radar is designed for a very high effective radiated power (ERP).e. by using high transmitter power or high antenna gain or both. The substantial transmitter powers radiated by most modern radars allow them to be detected by relatively modest intercept receivers in both their main lobes and side lobes.6 Burn-through technique. Thus a radar can detect a target up to its burn-through range (i. in which a radar increases its energy on the target in order to increase its ability to detect that target in a jamming environment.8 Low probability of intercept (LPI) technique.1. Burn-through means appearance of a true target on a radar indicator in a jamming environment. a burn-through mode is an ECCM technique.9 Frequency agility.1. Some of the spectral ECCM techniques are discussed in the following. Frequency agile radars are difficult to jam. the design of an antenna is made in such a way that it produces low side lobe levels in its radiation pattern. 5. In low antenna side lobes. The jamming will be less effective because it will have to be spread over a wide frequency band. any target located at distances farther than the burn-through range cannot be easily detected by the radar. This technique refers to the radar's ability to quickly change its frequency within its operating band. The two most significant features associated with an LPI radar are the spread spectrum transmissions and the low antenna side lobes. The interception of radar transmission ultimately leads to vulnerability through the use of either ARMs or ECM against a radar. The denial of signal interception would protect radars from most known threats.1.

This causes the false targets to change their position on the scope.1.10 Doppler filtering. 5.1. to eliminate blind speeds in MTI systems or to increase the radar's capability or compatibility in a dense signal environment.11 Temporal ECCM This category of ECCM includes such techniques which are time-dependant or timebased.1. This ECCM technique is for use on a tracking doppler radar to detect doppler targets and to aid in defeating velocity deception techniques.e. This is a pulse radar ECCM and/or anti-interference technique for use on a search or track pulse radar to degrade the effectiveness of false target repeaters. Its implementation involves stretching the transmitted pulse and compressing the received pulse. and other related ECM techniques. 5. Doppler filtering is a radar ECCM and anti-clutter technique. It permits an increase in an average transmitted power (without increase in peak power) with no loss in range resolution. 5.14 Dicke fix.
. An MTI (moving target indicator) pulsed radar system uses a number of gates and corresponding narrow bandpass filters to discriminate moving targets from a background of clutter or slowly moving chaff particles. PRF (i. This is an ECCM technique to counter continuous wave jamming.13 Pulse repetition frequency (PRF) agility. swept spot-noise jamming.1. Pulse compression technique uses matched filter for discriminating against signals that do not correspond to the transmitted coded signal. In this technique.12 Pulse compression. An alternative to PRF agility is to change the PRF momentarily. 5. Following are some of the temporal ECCM techniques. This is an ECCM technique in which a pulse radar transmits long pulses to increase the energy on a target.1.. the rate of transmission of radar pulse) is rapidly varied at a random rate so that the false targets appear jittery or fuzzy on the radar scope. In essence. The Dicke fix or wideband limiter device can provide some clear unjammed ranges where the radar can operate efficiently. while still retaining the target range resolution of a short pulse transmission.5. so that the recovery time from the effects of the swept jammer can be rapid. which uses a wide-band IF amplifier and a limiter ahead of the normal bandwidth IF amplifier in a radar receiver.

The limit level is preset at approximately the peak amplitude of receiver noise. depending on the jamming environment. These undesired signals can obscure real targets on the radar display or overload a computer so as to degrade decisions on absolute detection threshold criteria. 5. a process of locating an emitter by using crossing direction-finding signals from multiple receiving sites based on passive detection). The netted radars can function as an excellent ECCM device. A comprehensive list of all radar ECCM techniques is given in Table 2. This device provides excellent discrimination against fast sweep jamming ( 10-500 MHz) usually something of the order of 20 to 40 dB. an air defence radar allows frequency diversity. A large number of ECCM tactics or methods have been developed over the years as a result of continuous improvements in radar design philosophy and signal processing techniques. without appreciable loss of sensitivity. since the enemy must counter every frequency if he has to succeed in denying the defence accurate tracking information.. For example.15 Constant false alarm rate (CF AR). This makes the functioning of radars possible in an environment where interference due to signals from clutter. followed by an IF amplifier of an optimum bandwidth. CFAR does not give immunity from jamming.
. 5. The radar netting has many advantages.1. But a single isolated radar almost never exists. a technique that is specifically designed to protect the receiver from fast sweep jamming. The bandwidth may vary from 10 to 20 MHz. CF AR docs not usually permit thc detection of a target if the target is weaker than the jamming. Only a few were discussed in the above paragraphs. The CF AR technique keeps the detection of false alarm rate constant when the radar is receiving these undesired signals. provided the central node has some sort of automatic radar data control and data extraction facility. increases the potential ECCM capability of the system. There are usually at least two or three radars that feed information to a central point from where the commander directs the conflicts in the battlefield.Dicke fix is. The basic configuration consists of a broad-band limiting IF amplifier. Ideally. it merely makes the operation in the presence of jamming more convenient by making the receiver less sensitive. This is a radar receiver ECCM technique wherein the receiver adjusts its sensitivity as the intensity of the undesired signal varies. rain. the central control must have infinite data storing and processing capacity so as to avoid the saturation of the system at any stage.16 Radar Netting Up to this point the discussion was limited to ECCM techniques which are applied to a single.1. jammers and other radiating sources are present. thus. isolated radar .e. often called a 'radar net'. Thus. Another advantage of radar netting is that it allows the defender to do triangulation (i. This practice of operating radars in many different frequency bands immensely complicates the ECM problem. This combination of radars. but it does attempt to remove the confusing effects of the jamming.

because both the presence of message and its contents are required to be protected during its transmission till it reaches its intended user. Second priority. The radio communication bands that are most commonly used by the military are---HF band (3-30 MHz).2 COMMUNICATIONS ECCM The second major military use of radiated electromagnetic energy is communicationssending of messages from one element of force to another. For example.
. of electronic warfare to communications is more complex than to other uses of electromagnetic radiations.There are also a number of cryptologic methods or encryption techniques to conceal the contents of the message from the enemy. Third priority. Minimise the possibility of extracting intelligence from such transmissions as may be detected. which deny. Some of the important ones are mentioned here. The relationship. VHF band (112-135 MHz) and UHF band (225-400 MHz). and the second is Cryptologic Methods. Maximise the chance of survival of communications facility against jamming--electromagnetic invulnerability. 'call signs'(to conceal the identity of the stations). Prevent the transmissions from being observed by the enemy at allimperceptibility (also referred to as low probability of intercept. are used for communication security . frequency changes and operating time changes ( to conceal the identity of operations) .inscrutability. pass words or authentication ( to maintain the genuineness or identities of the sender and receiver). The first is Operating Methods. There are a number of ECCM communication techniques to meet the above-mentioned priorities or requirements. Communication Security again has two parts. The Operating Methods are mainly concerned with common sense.5. whereas providing protection to the contents of message during transmission is the goal of Communication Security (COMSEC). Fourth priority.the understanding of the contents of friendly messages to the enemy even if he does get possession of them. Determining the presence of enemy message is the goal of Communication Intelligence (COMINT). on the order of priority or requirement. Normally. Maximise the chance of survival of the communications facility against the threat of physical attack-physical invulnerability. even if he does get hold of them. To counter an ECM. etc. if the location of a particular aircraft in flight must be concealed then 'radio silence' is imposed. which deny the enemy access to the friendly messages and friendly communication channels. First priority. LPI) . the communications ECCM equipment must adopt the following four doctrines or guidelines.

are less detectable and possess low probability of intercept. is placed as far forward as possible towards the enemy and null steers are used to cancel the effect of the jammer on own-side communication. In this the outputs from two or more antennas are so combined that a 'null' may be steered towards jamming signals or other interference.
. and thus provide a limited means of evading a jamming attack. which could take over the groundsat.2.2. They are relatively invulnerable to stand-off jamming.4 Command frequency change. 5. This technique.1 Encryption.3 Frequency hoppers. It reduces the intelligence value of an intercepted signal.2. inscrutability.8 Groundsat. This is an unattended on-frequency VHF repeater that can be used to confuse the apparent point of origin of a transmission. The jammer.2 Privacy.2.secured encrypted digital message. which is of an expendable type. 5. It is vulnerable to electromagnetic attack. though short of encryption. They change frequency when under attack. This technique provides low probability of intercept because no carrier is present. 5.6 Null steering. except in vulnerability to physical attack.7 Null steering with smoke-screen jammer. also plays an important role in the protection of a message to Some extent. This technique provides the survival of a communication facility against jamming.2. electromagnetic attack.5 Single sideband (SSB). 5. Slow and fast frequency hoppers are the current ECCM 'fashion goods'.5.2. which can hence deflect the physical attack. it is of great value in a tactical environment. 5. but they are vulnerable to modern direction finders.2. This is a very powerful technique for imperceptibility. 5. This technique has got much recognition due to the fact that even if it protects the message only for relatively short intervals.2. 5. The message is semi-secured and often it is of analog type. This technique uses a 'clean jammer' on one's own working channel. because the enemy fails to understand fully.

2. 5. will be one of the major challenges for battlefield communications in the 1990s and beyond. The millimeter wave region (30-300 GHz) consists of a number of bands. Also.10 Millimeter wave (MMW). The management and integration of large amount of data. Digital source coding. great resistance to electromagnetic attack is achieved at the cost of complexity. Electromagnetic (EM) attack can be a disaster.12 Source coding. which is a very difficult task. Spread spectrum produces very low energy density per channel in narrow-band receivers and per frequency band in wide-band receivers.2. The management and integration of large amount of data. 5.By adding a null steering device to both groundsat and receiver. 5. increasingly of disparate origin and type. It can.9 Spread spectrum.
. increasingly of disparate origin and type. new and more sophisticated technology is being called into use. 5. but steerable notch filters can combat EM attack by line spectra. This technique uses the ionised gas trail produced by very small meteors entering the atmosphere to reflect VHF transmissions. will be one of the major challenges for battlefield communications in the 1990s and beyond. So.11 Meteor scatter. the ECM system must be prepared to jam all the bands.2. therefore. The battle of electronic warfare-ECCM against ECM-thus continues and every day. be entirely undetectable. new and more sophisticated technology is being called into use. they provide increased immunity to unwanted detection. Such longrange transmissions (say 1000 km and above) are difficult to jam or intercept. which involves irregular 'burst' data transmissions of short duration but relatively high data rate provides low probability of intercept. and thus provides a low probability of intercept. by using smokescreen jammer and the groundsat with the null steering. Spread spectrum technique gives protection from interception and jamming. The battle of electronic warfare--ECCM against ECM-thus continues and every day.2. Without prior knowledge. an unusual all round ECCM capability is achieved.

Man Went here and there in search of competent doctors and continued his struggle to find suitable medicines for the recovery of the radar. He wanted to see events happening at still farther distances. as shown in Fig. etc. CFAR for Constant False Alarm Rate. ground returns from trees. During the early days. The reactive nature of the EW field as a response to the enemy's initiative is well known and serves to generate the requirements on which the present EW systems are based. The radar operator has also now
. etc. provided a remote. water tanks.15. The learned specialists immediately came to the rescue of the radar with a full dish of 'alphabet soup' of Fig. long distance. There was nothing to see or hear of interest.effects. This resulted in the discovery and development of many kinds of medicines (now called anti-jamming or ECCM techniques). Long experience and widely held expectations in the defence and other interested communities indicate that EW will dominate the battlefield of future. At this stage. called 'natural' ECMs-clouds. ground vehicles. 13. This alphabet soup contained
many ECCM techniques which were named after the abbreviations of many antijamming (AJ) techniques: ASB for Angle Sector Blanking. Pity the radar operator in Fig. He tried to increase the detection range by increasing the sensitivity of the radar but it resulted in many unwanted side. MLC for Main Lobe Canceller.1 EW-A CONTINUING STRUGGLE WITH NEW DIMENSIONS The history of EW development has been quite interesting and challenging. MTI for Moving Target Indicator.6. began to make radar scope watching quite unpleasant. Radar was the first important development made by man after a long struggle with the application of radio waves in warfare. Later on. PIE for Pulse Interference Elimination. Man was not fully satisfied. LORO for Lobe-on-Receiver Only. the advent of intentional ECMs like jammers and chaff made radar scope watching worse. IFC for Instantaneous Frequency Correlator. 6. all-weather eye. 14. etc. mountains. on land. sea and in the air. ACET for Automatic Cancellation of Extended Target. the radar instantaneously became all right.. the radar clearly required some medication to get cured from such a serious ECM disease. radar when used in warfare. Current and Future Trends in EW
The discussion of EW will remain incomplete if we don't discuss its current and future trends. They poured this soup into the radar. These unwanted disturbances. As a result of this. SLC for Side Lobe Suppression. and un-intentional man-made ECMs-returns from buildings. Observation of warfare events on a radar scope was really a pleasure for the operator. ZCC for Zero Crossing Counter. FTC for Fast Time Constant.

16.1. as shown in Fig. It is difficult to enumerate all the areas. Man is continuing his struggle ceaselessly at many new fronts or dimensions of technology to get a more lasting or permanent solution to this EW problem.largely recovered and started watching warfare events with more renewed interest. Most of the world research efforts are focused around the following mission areas.
• • • • • • • • • • • •
Radiation detection and sorting in a dense signal environment Stand-off jamming for wide area penetration of enemy radar with minimum risk to the attacking force Extension of EW spectrum coverage to millimeter and optical wavelengths Decoys Airborne early warning and illumination warning Obscuration aids Radar and infra-red cross-section reduction High speed signal processing Microwave phased arrays Artificial Intelligence Simulation EW Integration
Each of these key or mission areas of research and development is correspondingly supported by a technical approach. as follows.
•
Development of high speed. However. This interactive problem of ECM and ECCM is thus still going on. But the disturbances due to many intentional problems in warfare is not over for him once for all. real-time Spectrum analysis by use of acousto-optic processing for100 to 1000 simultaneous spectral outputs
. there are some key areas which can be taken as most important and critical to a country's defence.1 CURRENT EW AREAS OF RESEARCH AND DEVELOPMENT Due to the complex nature of the subject there are many and varied areas of research and development in the field of EW today. The radar operator will still have unpleasantness of one form or the other.
6.

1. transmitter. sophistication and handling. including a digital phase shifter Development of expert systems for automatic EW data processing. EW antennas are different from other types of antennas used in radar or communications. in addition to imparting training to EW systems operators Development of systems which integrate IE0/IR/RF sensors and jammers into a single hardware. surface-acoustic wave (SAW) devices. are expected to generate a wide spectrum of technologies upon which the present and future EW systems will be built. 6. Use of gallium arsenide for even higher speed and strategic levels of radiation hardening in the digital area. and acoustooptic Bragg-cell diffraction for spectrum analysers and correlators in the analog area. use of fibre optics in delay lines.3 EW Antenna Technology Almost all EW systems require some form of antenna. chaff and pyrotechnic flares Development of C3. airborne early warning and laser-warning systems Development of aerosols and smokes that are effective over optical and infra-red spectra Development of low observables and stealth concepts. by their broad-band. signal processing and other associated subsystems. These technologies show great promises and are expected to bring changes in future EW systems in terms complexity. These technologies mainly relate to functional parts of EW systems and other interrelated weapon systems. the discussion is confined to a number of special topics that are related to the leading edge of today's EW technology. An EW antenna serves to couple transmitter signals into free space and receiver signals from free space into the EW system.1. wide-angle coverage and diverse beam and a radiation pattern with appropriate polarisation characteristics which has the desired
. receiver. charge-coupled devices (CCDs) for correlators and filters.
6. submicrometer silicon technology..2 LEADING EDGE OF EW TECHNOLOGIES The various key areas of research and development as mentioned earlier. such as structure geometrics and absorptive coatings and paints that avoid high reflection Development of very-high-speed integrate circuits (VHSICs). threat analysis. evaluation and development of new EW concepts and techniques. resource allocation and decision-making Testing. In the following. signal processing and other EW applications Development of monolithic solid-state transmitter and receiver modules. like antenna.• • • • • • •
• • • •
Development of programmable high-power broad-band microwave amplifiers and high-gain radiators Development of tunable components suitable for power covering millimeter and optical wavelengths Development of expendable jammers.

1. Many more antenna developments are in progress..g. etc. There are now two dominant types of TWTs-the helix TWTs and the coupled-cavity TWTs-which are found useful for ECM applications.5-8 GHz bandwidth can give 200 W power and at 7. first the threat information content of an RF signal is stored in the digital memory .. narrowbeam antennas for stand-off ECM missions. 6. dipole array antennas. The coupled-cavity TWTs used in narrow-band operation are considerably heavier. They are extensively used for stand-off jamming applications. in ECM systems. but are capable of much higher power operation than the helix TWTs. high gains. particularly at frequencies above 10 GHz. helical antennas. ease of modulation in the amplitude. power management concepts called for versatile RF transmission capabilities which could rapidly switch from one mode to another. expanded. travelling-wave tube (TWT). broad-beam antennas for ESM applications and mechanically scanned or switched wide-bandwidth. log-periodic antennas. low side lobes and optimum signal-to-noise ratio in the presence of noise sources. The heat dissipation properties of the helix structure generally limit the power handling capability of this type of TWTs. But the mechanically scanned antennas are ineffective for simultaneous handling of multiple threats. frequency and temporal domains. In this. ECM jamming systems that evolved prior to 1970 generally employed cross-field type transmitting tubes (e. In addition. etc. As the threat. Emerging technology is playing a key role towards the improvement of size and performance of these components. wide-beam-width. it became apparent that noise jammers needed to be supplemented with deception type jammers. multiple threat handling capability. Most of the EW systems in use today use fixed. To overcome this difficulty a new technique called 'electronic steering' has been devised. magnetrons and carcinotrons) which were used in noise jammers.4 EW Transmitter Technology Three main components. horn antennas. DRFMs are basically threat waveform storage devices which are capable of being used as exciters in a jamming transmitter. Atypical TWT operating at 2. which is quite common in a modern threat environment. This system provides wide-bandwidth.spatial coverage. VCOs allow a jammer to effectively function in a high signal density environment and respond to a variety of multiple threats. This led to the extensive use of TWT amplifiers. The electronic steering of an ECM transmitting beam is achieved through two approaches-the phased array and the lens-fed multiple beam array. which provided attractive characteristics like wide bandwidths. are associated with a transmitter power source. high efficiency. like spiral antennas. voltage controlled oscillator (VCO) and digital radio frequency memory (DRFM).The signal can then be reconstituted at some later time by sampling the digital memory. where maximum power is more critical than bandwidth. There is no currently available technology which has the potential to supplant the TWTs in the
. The helix TWTs are used in broadband operation for self-protection ECM applications. TWT is a versatile source of RF power generation.5-18 GHz can give 100 W power. There are wide varieties of EW antennas.

An ideal VCO should have fast settling times. These are critical areas on which the developmental efforts are concentrated. today it is touching the range of 1. replace moderate power TWTs (e. linearity. For example. 2-20 GHz). much efforts are being made towards the improvement of their performance in terms of broader bandwidth. in the near future. higher efficiency.The EW threat scenario for a receiver is changing day by day. the growing developments indicate that GaAs FET amplifiers may. the VCO should be able to tune in 50 to 100 ns and have a set on accuracy of the order of:t I MHz. Thus. high power FET amplifiers have been accomplished through power combining of multiple FET devices and using internal power matching techniques. staggered
. the pulse density used to be about 40. Only fast settling time to the incoming frequency can allow the following of frequency agile radars.000. To be effective. small size and weight. The most basic oscillators used in VCOs are transistor multiplier oscillator. particularly for wide-band use. Advances in gigabit digital logic using GaAs technology is expected to increase the instantaneous bandwidth to the 1-2 GHz region or beyond. but today it fluctuates in many modes--stable. during 1970s. Thus.g. the frequency range in 1970s used to be some selected portions of 2-12 GHz. but today the range is of the order of 40 GHz. In some cases. broad frequency band operation. the pulse repetition interval (PRI) in 1970s used to be either stable or multiple pulse trains. 6. but. DRFMs are key components of modern deception ECM systems. low posttuning frequency drift and accurate frequency repeatability. Similarly. They have instantaneous digital bandwidths of the order of 400-600 MHz and threat storage capability for this bandwidth of the order of 50-75 µs. In addition to this. At present most ECM systems use TWT transmitters. etc.1.. The main disadvantage of FETs With respect to TWTs for EW applications is that TWTs can ultimately supply far more power. In this.foreseeable future. Also.jittered. greater packaging density.. and lower noise figure.000 to 10. However.000. However. less cooling required. FET amplifiers offer a number of advantages over TWTs in the areas of reliability.g. Gunn oscillator and FET oscillator. 40 to 50W (CW)). increase of instantaneous bandwidth is the critical area of development. the present stateof-art generally restricts their use to low or moderate power applications. recent development of solid-state gallium arsenide (GaAs) field-effect transistor (FET) amplifiers have made the use of these devices practical for ECM transmitters which operate in the mid-to highmicrowave frequency range (e. and eventually challenge high power TWT amplifiers in the over 100 W class.000 pps (pulse per second).000 pps. higher power capabilities at higher frequencies. low-voltage operation. These potential advantages have resulted in considerable developmental effort aimed at increasing the power output of GaAs FET amplifiers.5 EW Receiver Technology The high threat density confronting the modern EW receiver is the driver of receiver technology .

1. dynamic range. for example. microwave low noise amplifiers. They exhibit relative advantages and disadvantages in terms of sensitivity. large time bandwidth product radar signals. requiring the enemy to diversify his EW resources. Small sizes of the devices due to extremely small wavelength or equivalently the high antenna gains of the small
. increased duty cycles with lower peak power. to handle a specific threat situation. but today it is facing more complex radar features. proved an effective technique in the Mid-East wars. a wide variety of EW receiver architectures are employed as described in Chapter 2. simultaneous signal resolution. Microwave multiplexing filters. coded modulations. spread spectrum. An EW receiver covering frequency ranges 100 MHz-18 GHz.. it is evident that no single receiver can handle effectively such a dense electromagnetic environment. for example. etc. bistatic operations. These components represent the key technology in EW receivers. high stability and excellent broad-band characteristics allow the construction of a large number of continuous bandpass filters and matched filters.or pseudorandom. pin diode switches. Their small physical size. digital processing. power management. Also. intra-pulse phase shift. etc. E0/IR techniques offer a number of advantages. laser. the wavelengths used are well separated from RF and MW portion of the spectrum. frequency hopping. which are most suited for real-time spectral analysis. weapon systems using multimode seekers (IR. E0/IR signatures are typically multi-faceted. The modern EW designer or system planner who ignores the E0/IR portion of the spectrum does so at his own peril. The use of optically-guided anti-tank weapons. frequency accuracy. 26-42 GHz and 88-120 GHz consists of several components. 6. selectivity. E0/IR ( 1200 Kilo GHz20000 GHz) has thus earned an important place in EW. Surface acoustic wave (SAW) delay lines are the key components of channelised and compressive receivers. local oscillators and fine channelisers using SAW filters are the most commonly used key components in the design of a microwave EW receiver. particularly as a response to radio frequency (RF) and microwave (MW) countermeasures. bandpass filter channelisers. Most modern EW systems have replaced low-noise TWT amplifiers used in older equipment with wide-band low-noise RF solid-state pre-amplifiers which have high sensitivity. during 1970s the EW receiver used to confront such radar features as single frequency . probability of detection. signal processing can be accomplished in the spectral. multiple agile antenna beams.6 EW at Optical Wavelengths The role of electro-optic/infra-red (EO/IR) techniques in modern EW has become increasingly important in recent years. doubly balanced mixers. Many developments are taking place in low noise amplifiers and SA W delay lines. capability of handling frequency-agile signals. Not only this. inter-pulse processing. susceptibility to ECCM. RF). From the above description. temporal and/or spatial domain. like multiple frequencies. To meet the challenge of complex threat scenario. design reliability and cost.

Major problems lie in target background discrimination. like smaller antenna diameter required as compared . Developments in sources (such as laser).1. detectors and signal processing are expected to give the system designer new flexibility in achieving high goals of exploitation of the total electromagnetic spectrum. their operation can be improved. increased immunity from unwanted detection. acquisition. The MMW system is not blinded by smoke. the recent emergence of laser threat has made the need for the development of laser-threat warning and response systems more urgent. They find most promising applications in fire control. clouds. The E0/IR systems thus find valuable applications in missile warning. pyrotechnic flare which acts as a false target or as a decoy to the approaching heat-seeking missile is the most effective countermeasure used today. particularly for target acquisition and fire control. E0/IR is playing a key role in detection and signal processing techniques. that is. precipitation and humidity can degrade or even negate an optical system.:red (EO/IR) systems currently used in the battlefield. optical channel obstacles m the atmosphere under water and dust. night vision. Also. The high antenna gain and accompanying narrow beam width in MMW systems make them useful for efficient search of large volumes. fire control. surveillance. In addition to this.
. fog or other atmospheric obscurants unlike the E0/IR systems. these advantages are tempered by some drawbacks that can be of crucial importance in operating conditions. The E0/IR system primarily suffers from lack of allweather capability. missile guidance and counter mortar/artillery location. however. Also. However. Many development efforts in all these key areas are currently in progress. The emergence of heat-seeking missiles has put more emphasis on the development of more pyrotechnic flares. optical systems are limited to line-of-sight applications. Currently missile guidance is the most potential application of MMWs. engineer and build.apertures used provide additional advantages. the optical surfaces are notoriously sensitive to dust. over-the-horizon communications. increased angular resolution. smoke and other particulates usually found in a battle area. due to their high angular precision and narrow antenna beams.7 EW at Millimeter Wavelengths (MMWs) Millimeter waves (30-300 GHz) present new opportunities for a number of EW techniques. reduced chaff illumination volume and smaller and lighter RF components. The E0/IR systems are expensive to design. The heat-seeking sensor on missile systems is the most lethal utilisation of E0/IR technology. MMW systems offer a number of other advantages over MW systems. increased Doppler sensitivity. 6. This emerging set of applications of MMW systems is an adjunct or replacement for electro-optical or infra.to MW systems for same antenna gain/beam width. In addition. improved low-angle tracking. increased beam width. laser designation and ranging. with simplification of components and improvement in functions.

protection or stand-off ECM system in a radar jamming situation is a function of the ratio. which is not
. If low observable technology is carried to its ultimate limit. Also. Also. It is well known that the effectiveness of a self. which are most effective countermeasures against current MMW systems.1. the jamming ERP required to screen it from enemy radars is reduced by the same factor. cost and weight of the ECM components and increasing reliability . if the cross-section of a military aircraft is reduced by a factor of 100. an ECM system requiring large complex. Atmospheric attenuation can actually reduce the amount of jammer effective radiate. it is called very low observable or 'Stealth Technology'. MMW radars cannot be expected to provide the detection/tracking range of MW radars. Another limitation of MMW systems compared to MW systems is that several ECM techniques which are successfully employed in the MW region such as chaff and radar camouflage are apparently less effective at MMW frequencies. /Peff where is the shielded target's radar cross-section and Peff is the ECM system's effective radiated power (ERP). Both low observables and stealth technology play key roles in ECM systems. The desirable effects of low observability are made clear in the following description.Low observable aircraft can penetrate through a dense threat environment to accomplish a mission. This behaviour provides several desirable effects in favour of low observable technology. A number of ESM systems which operate against MMW radars are currently under development. however. In other words. chaff dipoles made of aluminised glass fibres tend to become too small to be practicable above 35 GHz. parallelly. particularly the MMW ECM systems. for a selfscreening range or stand-off jamming range.However. It produces many desirable effects that find use in ECM applications. 94 GHz. 140 GHz and 220 GHz. many investigations are going on in the development of suitable aerosols and smokes. Thus. ESM/ECM does not offer a significant problem to the MMW radar designer. and thus above 35 GHz spectral reflecting particles such as aerosols are required to be effective against MMW radars. 6. the MMW systems do have' some limitations. at this stage of technology. The effects of propagation attenuation at these frequencies must be considered while designing. They also show propagation attenuation at certain frequencies like 35 GHz. Low observable technology in this case provides the same level of ECM effectiveness while' reducing the complexity. In particular. the amount of required jammer ERP is therefore reduced in direct proportion to the reduction in cross-section.8 EW Low observability (or Stealth) Technology The reduction of cross-section of a vehicle to escape detection falls into the class of techniques called 'low observables'. the allocation of some absorption regions of MMW spectrum to raiders makes them quite attractive for LPI applications. high power jamming transmitters can be replaced with a system that is entirely solidstate. For example. The propagation effects of MMWs are severe. An aircraft is considered a low observable if its cross-section detectable by a radar can be reduced ten-folds. They are inferior to E0/IR systems in angular resolution. However.d power (ERP) required to jam a MMW radar in a self-protection ECM mission.

In the next decade.1. curved surfaces without any sharp discontinuities to the airborne vehicle. The only serious limitation of fibre optics is that if a fibre is damaged in the operation of a system. still highly classified. 6. it is difficult to replace it immediately. One form of anti-radar Covering absorbs the incident radiation such that reflections are suppressed. The third method is by controlling the reflected energy such that it is re-radiated away from its direction of arrival. ground loops and cross-talk. This is achieved by reducing drastically the radar cross-section of a target vehicle. lightweight replacement for wire. Thus low observable technology is expected to play an important role to improve the ECM effectiveness of current and future military aircraft. the great bandwidth potential of fibre optics will provide the EW systems designer with low loss. The second is through the use of anti-radar coverings. however.possible with a conventional aircraft. By developing the necessary electronic interfaces and special purpose fibres. fibre optic components and subsystems offer the system designer new tools to address the complex issues required for physical and functional survival in the hostile operational environment that will be encountered ill the final decades of the century. It has been stated in the literature that stealth technology will be incorporated to some extent in all future US military aircraft and missile systems. interception. extended to a number of other fixed and mobile systems in which the fibre can be used to separate sophisticated signal processing from expendable portions of the weapon system. Stealth technology is used to make an aircraft virtually impossible to be detected or intercepted. There are apparently three methods for reducing the radar cross-section of an airborne vehicle. Another form uses interference coatings such that the incident and reflected waves mutually cancel.As EW systems become more densely packaged and use high data rates at greater bandwidths. Its radar cross-section is reduced to one-thousandths of a B-52 s~rategic bomber. The air-launched cruise missile has significant stealth technology. the applications of fibre optics will grow beyond the role of being simply a noise-free. lighter weight systems with high reliability and survivability . The concept used in the fibre-guided missile can be. The first is to provide small radii. Their use in transmission lines and signal processing is under investigation for EW applications. Fibre optics has the ability to transmit great amounts of information over long distances with low power consumption and to provide immunity from electromagnetic interference. Many details about stealth technology are.
. Fibre optics is currently finding use in fibre-guided missile system.9 EW Fibre Optics Technology The emergence of fibre optics has opened a new window to the world of EW technology . light-weight delay lines and antenna feed systems in which a single fibre transmission line will cover the complete electromagnetic spectrum from audio to microwave. Fibre optics also promises lower cost.

Further. each sensor can make its unique contribution to the overall mission success. into a single hardware is another emerging design technology for the future EW systems. silicon on sapphire (SOS). A number of EW signal processors using VHSIC chips have been designed for intercepted signal analysis. precision guided missiles and microprocessors. To be more cost-effective. Integration can also provide defence against anti-radiation threats and optimum use of ECM.11 EW Integration Technology The integration of E0/IR systems and RF systems. radar. Such integration allows multi-sensor fusion and correlation which vastly improves total system performance and reliability. More advanced EW signal processors which can function effectively in a dense signal environment are under development. as shown in Fig.1. EW systems have been stand-alone systems in most of the applications. For years. 6.1. WAM (window addressable memory). the integrated use of EO/IR and RF allows the optimum deployment of expendables and monitoring of their effectiveness against a threat.10 EW Signal Processing and VHSIC Technology The present VHSIC technology thrust is aimed at meeting the high speed. N-type metal oxide semiconductor (NMOS) and oxide isolated bipolar (OIB). low power consumption and military environment operation signal processing requirements in EW. Now there is a trend and EW requirement to combine the RWR and ECM into a single system.6. integrated EW /EOW is used as a force multiplier.
Also. like the CAM (content addressable memory). Not only this. various elements such as radar warning receivers (RWRs) and jammers in tactical aircraft have been separate and distinct systems with little or no interface. By integration. serious efforts are being made to integrate elements of EW and the weapon system or platform to gain overall control of the dense signal environment. communication. etc.
. 17. Semiconductor technologies represented by VHSIC chips incl~e such classes of technologies as complementary metal oxide semi-conductor (CMOS).

but the only means short of war. The inferences then allow the computer to interact with the knowledge source (e. In contrast. its effectiveness can only be demonstrated in the presence of a real or fully simulated combat environment. together with the advent of increasingly complex EW systems. has a lot of potential use in future EW systems. For example. when accurate data is used to simulate the performance. Simulation technology serves many important functions in the field of EW. thus. AI. The reality of present AI applications is that they allow the implementation of a smart adaptive computer program. since EW is primarily intended to thwart or deceive the enemy. to act as an expert adviser to decision makers in C3I and C3CM systems. in the case of EW. it provides a practical mechanism to assess the effectiveness of the developed EW systems or hardware.1. it is possible to say with a high degree of confidence whether one's own new development will be effective or not. It has been identified as one of the important military technologies of 1980s. Recently. sensor resource allocation and planning. EW simulators are important in many ways. they are useful in the development of new concepts and techniques to counter enemy radars and weapons.
. surveillance and intelligence data processing and threat assessment.g. Several applications of AI have been identified in the field of EW. Also. 6.. EW simulation involves1he presentation of EW data as would be encountered in a realistic combat environment. and information retrieval and routing. Similarly. alternative jamming techniques.12 EW Artificial intelligence Artificial Intelligence (AI) has added a new dimension to EW AI is an evolving computer technology which in the broadest sense attempts to capture in computer software the processes by which humans solve problems. rather than provide destructive effect. Traditional weapons can be tested and evaluated by firing against targets to prove their effectiveness. The growing importance of EW in both strategic and tactical roles in modern combat philosophy. These include the fusion of multi-sensor data as a decision aid to threat analysis systems. their operators may be trained on the firing range. simulation is not an alternative method. Further. of creating a realistic environment for evaluating a new receiver.6.1. In other words.13 EW Simulation Technology Simulation generally means recreating a situation or environment for study and analysis of problems. signal processor designs. user or input sensors). which can examine stored data and action on rules to draw inferences about the data. AI has been used to compile and monitor the hostile air defence electronic order of battle (EOB) in support of a mission while penetrating enemy air space. have made it necessary to devise new and effective methods for the evaluation of equipment and the training of personnel. to request new data in an iterative manner until a conclusion is reached. reconnaissance.

movement. but the relatively low-cost minicomputers have opened up a great many new field5 of application. tactical or theater.14 EW in C3 Systems The ability of a military force to exercise command and control over its individual units. A number of EW simulators have been developed in many advanced countries like USA for various purposes. and activities of enemy and friendly military assets Navigation subsystems which inform friendly forces of their own location Command and confusion centres which assemble. 6. and naval EW training simulator (NEWTS).
An air defence system like Airborne Early Warning aircraft is the classic example of a command and control system. they also happen to be the most expensive (30-90 million dollars).optimisation of ELINT . as well as effective countermeasures to enemy ECM. Control and Communications (C3) system or simply known as Command and Control system.AWACS is the only system that can effectively provide vital command and control functions in a wide range of strategic and tactical missions through the entire spectrum of peace to war. Although AWACS are among the most effective air defence systems available today. Formerly. such as dynamic electromagnetic environment simulator (DEES). to communicate the basic data on minute-by-minute events to its control centres. The latest development in this class is the AWACS (Airborne Warning and Control System). in short. and commands back again is considered to be one of the most vital factors in the success of modern warfare. Due to the significant advances in modern technology . Any C3 system. The advent of minicomputer and the recognition by design engineers of its tremendous flexibility have both had a great impact on simulation technology. AWACS. whether strategic. integrate and display enemy and friendly force activities to decision-makers. consists of the following basic elements.
• • •
•
Sensor subsystems which gather information about location. long-range surveillance ( detection. This concept is commonly called Command..
. tracking and advance warning) of high-or low-flying aircraft (hostile as welt as friendly) .1. in a large volume of air space. provides full. air force EW evaluation simulator (AFEWES). Many command and control systems are also characterised as C31 systems. both size and cost considerations had restricted the use of computers to huge simulator systems. checking ESM system performance and for training EW system operators. who then assess the threat and command appropriate response Communication links between the sensors and command centres and between the command centres and the forces to permit the transmission of information and commands.

when neutralised. jamming protection may be achieved by employing such concepts as low probability of intercept. The neutralisation of C3 systems is accomplished through the use of C3 countermeasures (C3CM). but have extended their influence. in modern warfare. as shown in Fig. redundancy and operational procedures. decoys. ECCM. destruction protection of a C3 system may be achieved by employing such concepts as mobility. deception. EW is a subset of C3CM. provides a means of neutralising a hostile force (force divider effect) while concurrently enhancing the power of a friendly force (force multiplier effect). an ECCM activity similar to that employed with radar and communication sensors. jamming. a force divider effect is accomplished. mobility . hardening. distributed architecture and covertness. According to the modern concept of warfare. Man's conquest of space has brought a new dimension to arms technology . bistatic operation. aims at the neutralisation of an enemy's C3 system while ensuring the capability of operating one's own C3 system. When C3 systems are employed as force multipliers they become prime targets for enemy attack because.1. to the space also. and deception protection may be achieved through such concepts as COMSEC. communication systems and method of surveillance with consequent innovations in the field of EW. The basic methods employed with C3CM are exploitation. covertness. mobility and operation procedures. exploitation protection may be achieved by employing such concepts as communications security (COMSEC). but also to protect its own friendly C3 system from the enemy's destruction. The basic aim ofC3CM is not only to neutralise the enemy C33 system. EW thus. redundancy. jamming. For example. To make the C3 system ineffective. and passive operation. jamming and destruction. which when used in conjuction with other military assets.where I stands for Intelligence. 6. EW is considered as one of the basic elements of an overall military strategy . exploitation or deception. decoys. 18. EW plays an important role in the operation of modern C 3systems.15EW in Space The activities of EW have not been confined to battlefields on the Earth alone.
. the overall system may employ any method like destruction. netting. To protect the friendly C 3system the overall system may employ a host of other methods. exploitation and deception. With this framework.

Since 1958. He said that the United States would abandon the old strategy of detente achieved through the threat of massive nuclear retaliation and would pursue a new strategy based on the ability to prevent nuclear war. NASA is planning to set up a permanent space station and an Electronic Warfare Command and Control Centre by 1991. . targeting. reconnaissance. The system has many ECCM features built into it like frequency hopping over a very wide bandwidth. There is a growing race between ECM and ECCM systems employed in space by the Superpowers. and electromagnetic pulse (EMP) effects. Ronald Reagan in his famous 'Star Wan' speech. and a host of other intelligence functions. COMSEC/TRANSEC and sophisticated signal processing. weapon control.The use of satellites for military purpose began in 1958 when the United States launched the communications satellite SCORE which simply transmitted a pre-recorded message from space. have been launched by the USA and USSR alone. in particular . there are a number of anti-satellite systems today. spacecraft proliferation and high-altitude orbits.the United States is building systems like the MILSTAR (Military Strategic. to active missions requiring reliable operation during warfare. These weapons would be 'directed energy' weapons. To defeat the Russian jammer system. obtaining information on specific transmitters and emissions. optical manoeuvering/evasion. high energy lasers.initially experimental and later operational. narrow-beam. Till now about a hundred reconnaissance and early warning satellites like Ferrets of USA and COSMOS of USSR have been launched for electronic reconnaissance on ICBM launchings in general and 'to gather electronic intelligence on friendly and enemy radars. In March 1983. evaluation of hostile force command and control procedures. officially announced a new defence doctrine based on space-age weaponry. A wealth of self-protection techniques are being designed into spacecraft to defend them against various levels of jamming. so as to have a secure world-wide satellite communications network free from all interferences including jamming and deception. updating of hostile force electronic order of battle information. ECM. The ELINT operations through satellites are conducted to satisfy a variety of military requirements like location of hostile elements. principally strategic intelligence gathering and long-haul point-to-point communications. warning. attacks from anti-satellite weapons. The Superpowers are already studying future
. To make the functions of ELINT satellites ineffective. orbital decoys.Tactical and Relay) EHF(Extremely High Frequency) satellite communications system which offers both extensive anti-jamming as well as laser and EMP hardening. survivable C3I. stealth or low observables. Military space systems are making the transition from their two-decade old role of mission support. nulling. detection.1'he most promising survivability enhancements now being reviewed for possible integration to next generation space-based systems are-laser shields. high-gain antennas providing excellent spatial discrimination. Space EW now includes and will include for many years to come the military EW functions such as surveillance. weapon delivery and target damage assessment. testing of hostile force ECM capabilities. It would be a defensive strategy employing weapons designed to intercept and destroy incoming enemy missiles. EMP hardening. the US President. more than 2000 military satellites.

electronic combat in space and 1991 is not far away. IR flares. ECM equipment similar to that used on Earth could be employed against the platforms onboard jammers and expendable jammers. satellites. it is obvious that EW mission requirements are pursuing two distinct EW design philosophies-the stand-alone EW philosophy and the suppression of enemy air defence (SEAD) EW philosophy. The era of space fiction is over. laser or IR source. Soyuz satellites. space will provide the perfect arena for a show of strength by the most technologically advanced superpowers in these new fields of military art and connected branches of applied science.g. From the discussion on the current EW scene. Many EW techniques have been evolved over the years to counter such threats. tactical communications. chaff. It is likely that in future international crises. I t has become a reality and a sort of electronic 'star wars' could be what the future holds in store--a space shuttle fleet fitted with high energy laser weapon systems patrolling the 'skies' ready to intercept and destroy enemy ICBMs still in their booster stage. is a carry-over from the electronic threat environment which existed from World War II through the mid 1960s. Both require threat warning receivers for immediate detection of enemy radar. The stand-alone EW. Of the $26 billion targeted for SDI (Strategic Defence Initiative) research for the next five years (1986-1991). Countermeasures against the platforms or space-stations (shuttles. ICBMs and radiation weapons. anti-tank weapons) against air. also called 'self-protection EW' design philosophy meets one type of EW mission requirement. of countermeasures to nullify the effectiveness of 'space-umbrella'. The threat in this time period
. The Superpowers are exploring the possibility of employing two types. which EW techniques are to be incorporated into or closely coupled to a hardware so as to make it effective against various threats. A crisis could be resolved in favour of the superpower who could control the space more effectively through the use of EW-based spacecraft. how they are to be interfaced with the rest of the system. The primary aim of EW in this mission is to provide protection or survival of the system against a particular threat. Current EW systems are viewed from mission requirement point of view. the crux of the EW problem since beginning. radar absorbing shields and so on. it is worth defending in space.2 CURRENT EW DESIGN PHILOSOPHY Design philosophy basically determines. in fact.) and countermeasures against directed energy weapons. naval or army platform is met effectively has remained. laser decoy mirrors and space mines of any other electro-optical countermeasures (EOCM) which may emerge from technology progress could be used. From the increasing influence of EW in space. first. etc. The stand-alone EW design philosophy. Against the laser beam. one can conclude that if one's way of life is worth defending in one's towns and villages. Design philosophy has primarily been the key basis for the development of all these EW tactics. 6. missile. How a particular threat {e. and secondly. USA has slated some S200 million for self-protection space-based systems studies.

6. well known in their principles of operation as well as frequency bands. even in a survival sense. The various companies around the world earn millions of dollars through sale of EW equipment. Sweden and Israel are the leaders in the EW market. which is directing the suppression mission. West Germany. In this design approach EW techniques from many platforms are combined with other non-EW military assets. The basic EW encounter was a one-to-one situation. Netherlands. The threat warning function is many times coupled with a defensive capability in the form of a self-protection jammer in combination with decoys. A number of EW companies with varied specialisations have come into existence to meet this growing demand.consisted of a few radar directed threats.
. are also going on in a limited scale to develop EW systems to meet the defence requirements of their own countries.. USSR. There is a tremendous demand for EW systems. However it is difficult for anyone platform (particularly airborne platforms which have weight limitations) to carry enough EW to encounter today's sophisticated threats.1 CURRENT EW WORLD MARKET The fear of war and potential of EW systems to handle such fears effectively has led to the establishment of many research and development organisations and production agencies in many countries of the world. A list of leading companies in the world and their I specialised EW products/services can be found in Appendix 2. China etc. and each platform carried the EW equipment necessary for success in this environment. Thus.2. UK. and degradation of enemy communication network in association with other systems. EW was then a single countermeasure taken against a thinly deployed (both spectrally and geographically) array of hostile weapons. which helps to degrade the overall enemy air defence C3 structure while preserving one's own C3 capability. is to neutralise certain critical enemy radar and communication links. C3CM plays an important role in SEAD mission. efforts in developing countries like India. However. Suppression of enemy air defence (SEAD) design philosophy is another EW mission requirement. France. This philosophy still exists and that is why. such as chaff or flares or which can divert weapons from the intended target. Many underdeveloped and developing countries will have to depend on foreign sources of. The primary aim of EW is to provide effective support to the C3CM mission. Advanced countries like USA. ships and troops) which operate against enemy actions have as a minimum requirement a radar warning receiver (RWR) with atleast quadrant threat direction-finding capability. development and production of state-of-the-art EW systems. Italy. current EW design philosophy is playing a key role in the modern warfare a~ both fronts-self-protection of the system by itself. Today EW has become a highly competitive market. The function of EW in this strategy. supply till they establish their own design. most current platforms (aircraft.